I don't have much written about it - I mostly post on "the other site" just because it is safe to say stupid things every once and a while ;-)
My impressions of the Cullen mods are basically simple.
Impressions made with RSP-1/RPA-1 Emotiva combo to Onix Reference 3 speakers
It made the soundstage extend out of the room l/r and made a much more stable center image. There is more depth in the stage. The separation between instruments has improved - everything holds its own place in space.
Bass has more impact now.
The overall sound is much more "real" now. The slight bit of digital edginess is now taken away.
This one of the first components that I noticed "burn-in". Bass was dry when I first received it after mods. I wasn't really blown away by it at first. There were improvements noticed right away, but not fully developed.
I think the gain cell technology is very cool and wouldn't mind my gcha being a pre-amp also!
Let me know if you have any specific questions. A lot of the components in my sig have changed, you are in my friends list on HF - so check my equipment list over there.