I've had the pleasure of using this great amp for a few weeks now and wanted to post some brief impressions. One interesting angle is that I've used it in all of its I/O configurations, gradually moving from the worst to best configuration. Equipment used is LSR305 with the 310 subwoofer, and HD6XX.
Unbalanced in/Unbalanced out - Compared to the Little Dot Mk3 headphone amp/pre-amp I was using before, I immediately noticed a really pleasing, smooth texture to the lower registers (everything from bass drums to bass guitars), and better detail.
Unbalanced in/Balanced out - Now noticing this amp really "singxing" (sorry), with a fullness through the entire frequency range that wasn't present with the SE out.
Balanced in/Balanced out - I also upgraded my DAC from a really old JDS Labs ODAC to a Topping D10 Balanced. Absolutely loving this setup, and noticing a lot of additional clarity. The detail around vocalist's vibratos for example is really apparent.
Overall I'm loving this configuration, and feel like it has achieved something I've wanted for a long time - a high level of detail and clarity but with warm and pleasing tonal qualities. Also worth noting that between my headphones and speakers, I'm actually enjoying the 305/310 combo with the amp in pre mode the most. I think it's hard to get away from what this rather musical subwoofer adds to the experience.