So I've had the 2100 here for a couple weeks now but have held off writing anything about it as I wanted to let the initial excitement die down. The verdict? I like it even more than I did when it first arrived!
It is magnificent and exceptional - slightly warm through the mids, nice sparkle in the highs and it has the best bass reproduction of ANY amp I have owned. It is a smooth customer...loud doesn't really seem loud till you look at the meters and realize you should be in pain, but no, just musical bliss.
I had a Luxman L-507u before the Yamaha and to compare I would say the Lux is slightly more dynamic and a tad more exciting while the 2100 smoother, more refined and musical. The 507 had some big bass but it was a bit boomy compared to the 2100. The bass on the Yamaha is tighter, deeper and I can seem to really pick out the bass tones better as oppose to the Luxman. Pick your poison, both are good but I am glad I sold off the Lux as it was 2x more expensive. The 2100 is a great amp and one of the best I've had.
UPDATE: I didn’t mention anything about the built-in phono stage or headphone amp because at the time I simply had not tried them yet. I am between TT’s right now but the phono via the budget model Rega I am borrowing from a friend sounds pretty good to me. I have not compared it to an external stage and the Yamaha’s limited settings probably requires careful cartridge selection but it sounds no worse than my previous amp’s built-in phono stage.
Headphone amp, well, it sounds great! Much better than the A-S1000 I have at work and every bit as good as my vintage CR-1020. The multiple gain settings are a plus should you have hard to drive headphones.