In terms of playback, so far it seems to handle large files okay - I've chucked some chunky hi-res stuff at it, and after adjusting the buffer settings playback was fine.
In case I said something misleading, the reference to 'large libraries' above concerned the quantity and organisation of files that the Pi has access to. I'm using Volumio at the moment, and the web-based UI is fine, and quite pretty, but it's a little impractical for me to use for browsing and selecting tracks to play, since it simply mirrors the directory structure of the NAS, and even though my files are well organised, the sheer quantity of album folders makes this a PITA.

Thanks Martin! I'm using the same Volumio build, so will give this a go. Though, I'm now venturing into very unfamiliar territory, so we'll see how far I get - I'll have to do some research

No worries Martin - it was more straightforward than I was expecting, and interesting to get under the hood a little.
Hope you're enjoying the US

It's good that it's that close between them, Tom. Did upgrading Linux help you with the clicks?

When I get the Digi I2S S/PDIF board for the B+, I'm expecting a notch up in SQ over USB. We shall see.

Yes I was surprised! I'm continuing to play from them both while I work, and occasionally switching between them - the difference really is subtle, and it may be that the Pi slightly edges the PC in other areas - the presentation seems slightly flatter with PC, though again I need to test this with more care.
Upgrading Linux does seem to have reduced, though not entirely eliminated the clicks - perhaps I have to fiddle with the buffer settings a little more.
Yes the Digi+ board looks great! I might get one also, as it will be useful if I want to deploy the Pi elsewhere in the flat.

Well the caveat is that I've not yet tested it against the PC outputting via the SOtM card - my suspicion is that the difference would then be less subtle, and entirely in the PC's favour. But that's as it should be given the price disparity. However, if the Pi were partnered with something like this then perhaps that would close the gap, as the ifi seems to address some of the same issues as the SOtM, just at a different point in the chain.

Ah well, I'm currently powering it with one of these:

www.justmobile.com/productdetail.asp?productid=32933

But this was just the one that we had lying around here, and I don't know if something differently spec'd might produce better results (way beyond my field of expertise here)

Quick update (in lieu of something more substantial): Finally got the Pi working with JRiver - now I can control it with either Media Centre on the laptop, or JRemote on the iPad - much much much nicer than using volumios web-UI. Very pleased!

Here you go!

So, I've been running the Pi for nearly two weeks now - here's some things that have happened so far:

As I noted above, I set out with the intention of running RuneAudio, rather than Volumio, but I didn't get very far with this. Once I'd established that the Pi's initial refusal to do anything was due to my trying to use a version of Rune that wasn't compatible with the B+ board, I flashed the micro SD card with correct version, powered up the Pi, and everything worked! Well, at least I could connect to the Pi via Rune's web-UI, and pointing it towards the NAS was straightforward enough. However, I couldn't get it to play any files correctly - whatever I played came out as series of distorted squelches. In other circumstances, this might be a nice thing - I have some music which sounds pretty much the same - but obviously something wasn't working correctly. So, after fiddling unsuccessfully with various buffer settings, I concluded that Rune doesn't get along very well with my USB interface. I have a couple of other DACs with USB inputs, so could test this some time, but wasn't in the mood to do it then, and switched to Volumio.

Volumio worked 'out of the box'. I tested it by pointing it towards just one music folder on the NAS, and it was able to play the files fine - no more squelching! So, after establishing that it worked, I pointed it towards the entire library. It took around two hours for it to build a database, but there's quite a lot of music there, so fair enough. Once that was done, I was able to use the web-UI to browse the library, and play and queue files.

One thing I noticed about the web-UI, is that - at least on the current version of Volumio (an older version had more flexibility here it seems) - the library structure mirrors the directory structure on the NAS, and does not make much use of the information stored in the files' tags. This isn't a huge problem for me, since I keep my files quite well organised, but I suspect it would be a problem for some. So, on opening the NAS mount, this is what I get:



You'll see I have the files organised first by genre, and then by album:



It looks nice, but a problem is that, with a big library (even a well organised one), this is still a very clunky way of browsing one's music, particularly compared to what I'm used to...

JRiver on the laptop:



Which is itself outdone by JRemote on the iPad:



So, from my perspective, this was a mark against the Pi - if digital music isn't convenient then, for me, it loses one of the key reasons for using it. So I did some research, and found this thread on the JRiver forums:

yabb.jriver.com/interact/index.php?topic=89044.0

This indicated that it should be possible to use the Pi as 'DLNA renderer' for JRiver. This sounded good, but then I didn't know what a DLNA renderer was, so I was unsure if this is what I was after. I then found a handy glossary here, and it seemed that what I really wanted to do was to use JRiver and JRemote as a DLNA controller for the Pi. I haven't figured out yet whether this is possible, but it seems that using the Pi as DLNA renderer for JRiver is in fact close enough to what I wanted. So, after reading through some relevant threads, and reading an old update on the Volumio blog, I discovered that - as of version 1.4 - Volumio is actually packaged with a DLNA renderer, so things were pretty straight-forward in the end (if only I discovered this before spending several pained hours with the command prompt...).

It's simply a matter of accessing the system settings via the web UI, and turning on 'UPNP Control'.



Once this is done, Volumio appears as a zone in JRiver:



And JRemote:



And then - whilst in this zone - I can browse the library as I usually would, and when I select tracks they're sent to the Pi. One thing I noticed is that, by default, JRiver is set to transcode lossless DLNAd files to high-quality MP3, which I wasn't very keen on, and the setting turned out to be quite well hidden (from me at least). Here it is:

Options > Media Network > ... Add or configure DLNA servers ... > Audio > Mode > Original



Now everything works perfectly! Although, I'm slightly unsure of the underlying process here - is the file still going straight from the NAS to the Pi, or is it going from the NAS to the Pi via the PC? I don't know.

One thing to check though is the comparison between the Pi playing a file like this, and it playing the same file from its own NAS mount. I don't know enough about this stuff to know whether to expect any difference, but the chap in the JRiver thread found that there was (though he was using a different renderer).

I still need to do some proper comparisons, and have a go at evaluating the Pi in terms of sound quality - maybe this weekend!