When I received the first modded amp, I compared it to the stock amp and reported that the modded amp sounds cleaner than the stock amp, without a doubt. The effect was analogous to adding a really good power conditioner.
Once I installed the second modded amp, I heard some "new" micro detail in the bass of songs I've played a zillion times. Other than that, the second modded amp didn’t make the same impact as the first one, but that’s to be expected. I can’t make any other claims beyond better bass definition and improved clarity/detail, which I’ve already described. The sound stage, imaging, etc. appears to be the same.
To elaborate on what I mean by bass definition – for instance, when the upright bass is playing, I can now clearly hear the subtle notes and sustained notes in between the apparent notes (sorry if I’m using the wrong terms here). Likewise with drums – when a drummer is riffing and going a hundred miles an hour, I can hear every strike of the drumsticks. I’ll bet that 99% of audiophiles aren’t hearing this. There’s no way a non-servo box sub can keep up with the speed of sound of a drummer while he’s groovin’, but with the modded amps, it’s now more noticeable.
I don’t have any measurement tools, so I dialed in the amps by ear. Upon first listen, I increased the phase a little. I think it's near perfect now. By the way, dialing in the phase is vitally important. The proper setting is where the magic comes from, where the music locks in.
Overall, it’s a great mod and worth doing when you’ve done everything else. Folsom was exceptional to work with, so no worries there. Maybe some of you guys will go for the Level 2 mod and report back.