It's all to do with gain in all honesty! I've used an active pre with the NVA amps here and been all but deafened in the process with the volume at not far off zero!

In reality, the NVA power amps are really about the same nominal sensitivity as an old Quad - I'm guessing around 500mV. A well sorted 33 which I have is lovely with my NVA amps (it did need a heck of a lot of work doing first to bring the sonics and noise to acceptable levels though). The Crown preamp, itself needing modern op-amps and a bit of signal capacitor replacement, sounded ok but just a bit 'pushy' to me - fine with the D-60's with gain backed off as recommended by the manufacturers. The biggest shock, and not in a good way, was the AVI preamp I have. With a usually good Class A driver stage biased and set with hot running transistors like a small power amp and very low output impedance, it should have been acoustically transparent with the NVA's, but using short interconnects it wasn't, sounding very 'forced' and thumpy if anything. In fairness, ask it to drive several metres of interconnect (to a remote active speaker) and it's as sweet as a nut for this task.

Last one I tried was my trusty old Croft 4PP. Didn't even come in the running as it altered the sound signal passing through it too much (it's an older design and definitely adds sonic softening and sweetening to the flavour, despite it being better than when I first bought it from the original owner - modern Crofts aren't as invasive)

After all that messing around and with all my power amps, even the Krell which is the least sensitive of them all at 1.3V or so, the NVA P20, let alone all the others, sounds better! I know some people like the 'push' of a good buffer stage and if the amps are placed near to the speakers, this can be an excellent way of doing things. NVA's as well as Naims I think, seem to like long speaker cables of the correct specification and shorter interconnects, although if you need two to three metres of interconnect with an NVA pre to power, I'd look at SSPmk2 as the capacitance is half that of SSC (and four times lower than SC) if I understand the maths correctly.

So to summarise - and apologies for the essay - a P20 won't break the bank and it loses NOTHING of the emotional contact with the music that NVA is so well renowned for retaining. Using CD, DAC and the Phono 2, there's plenty of level there, even with the Krell (and that WAS a surprise), it just means the volume control is used as it should be, a level matching device turned lower for NVA amps, half way or so for the Crowns and HH, which are around 750mV and well round for the Krell, still enough on Kraftwerk this lunchtime to get the bias lights on and the case cooking - ooops... those Krells, even with plateau biasing, run very hot indeed in their middle 'plateaus' and I fear for the internal capacitors as there are a lot of them...

I have to say, I'm becoming hooked on bigger-Krell bass. All in the power supply, but man, it's addictive on more dancy stuff.....