I just had a chance to speak with my brother regarding this (he is a professional audio engineer), and he had a suggestion I hadn't thought of to test the digital files for changes be they audible or not.
I imported both the treated and untreated copies of a track (using the previously imported Pink Floyd album) into Audacity to compare the waveforms, then inverted one of them so that and difference would be immediately noticeable on playback. The result? Upon inverting one track they canceled each other out perfectly resulting in silence on playback.
Now, all this means is that the files on my PC are 100% identical. These were imported from the disc as .wav with EAC then, also with EAC, exported as .flac for playback. This means that either that particular CD was not affected at all by the Nespa treatment (unlikely) or any improvement made was lost at some point in the conversion from disc to .flac. I'm going to play with my EAC settings to see if something there is at fault, and will also try comparing the raw .wav files on the next CD I test.
I'll continue looking into alternatives to converting to digital as well, since my end goal is to have my CD collection available for streaming. Hopefully I can come up with a solution, as if the improvements are only on CD playback that would throw a wrench in my plans.
Any suggestions on other things to try are appreciated.
I just tried again with another CD (Depeche Mode - Violator, 1990, first US pressing) after adjusting a couple EAC settings. I loaded the .wav files into Audacity without doing any compression or conversion and they still came back with 100% identical waveforms. It seems that, at least with my current optical drive and EAC, no change is appearing when converting to digital. I don't know if this just means that I am already getting the maximum quality I can get from digital (bit-perfect import) or if there is some alternative method I could use to get better. I think the bottom line may just be that, as MartinT said, the Nespa is meant for proper CD playback and does not have any observable affect on importing to PC.
Once I receive the Tascam and/or NEC CD player(s) I ordered I try out some non-PC listening and try to compare the CD playback to the digital file, just to see which sounds better. I may give real-time capture from the CD player (as opposed to EAC ripping) a go just to satisfy my curiosity and do some other tests as well.