I have an SB3 with all of the standard (original) mods. I currently don't have a speaker rig (it's in the works), so I've been listening to my music through a META42 DIY headphone amplifier to Sennheiser HD-580s.
Now, I'm stepping up to the SB3 from an M-Audio Sonica, a cheap USB DAC that runs straight off the computer's power source. That DAC was a huge step up from the noisy integrated soundcard in my laptop. Vinnie's modded SB3 is such a huge step up from the Sonica.
Sounds are sharper and more distinct. Everything is faster, and I now understand what people are talking about when they say "black background". More bass on the low end, and more extended highs. Other people have commented on strings heard through the SB3, and stringed instruments constantly pull at me with their reality and heft.
I'm not sure how long I've run the SB3 by now... probably 120 hours. I don't have anything high-end to compare it to, but it easily wipes the floor with all of the sources that I've used before.
I can't wait to hook the SB3 up to a real pair of speakers!