So, a brief comment on the A20 amp with the T1 headphones (as promised)...
It's gorgeous. The build quality is fantastic. Just turning it on, or plugging in your headphones is a little kinesthetic event, that gives you a subtle jolt of pleasure. The whole experience is reminiscent of getting in an expensive German sedan, slamming the door ("the sound... just so"), easing into the leather seat ("so comfy it's unremarkable"), pressing the "on" button ("a diesel so smooth you can hardly tell it's on") and slipping it into drive (<snick>).
That being said...
It's a $500 amp. I was expecting a vast improvement over the $120 Vali that I am otherwise using to drive the T1's with. It's probably just me, but I'm not hearing it... and after all I'm the one who's paying. It's not due to the quality of the source material (high quality FLAC), nor the DAC ($500 NAD D1050) or the headphones (T1). In fact, it's an amp that is specifically built to match the T-series headphones, and has gotten great reviews for the synergy with them.
I'm going to give it a week, because I really really want to like it better than the Vali, but at the moment I'm tending towards returning it before my cool down period of 14 days is up, and just sticking with the Vali until I notice it's limitations.
I'd be VERY interested in hearing your impressions of the Vali with T1s, or just of the Vali with high quality headphones in general. Perhaps I'm just missing something.
TL;DR: The quality is outstanding, but in my opinion the Vali is really exceptional value for money, and a surprisingly hard amp to beat this side of $500.
Definitely give it some time, dduck. I had a similar experience upgrading from the Bottlehead SEX to the Bottlehead Mainline. My initial impressions were a bit "meh", but as I spent time with the Mainline, its subtle excellence really shone through. The very best amps are often the most unremarkable on first listen because they balance all the sound so well that we don't notice what they're doing. Cheaper amps often have coloration or characteristics that make them more intriguing on first listen, but the better amps will often be better across a wider range of source material and genres over time.
Having said all that, I haven't heard the Vali or A20 so it could be a case of the Vali being an excellent value option.