I've used it for about a week, after buying it secondhand online by chance to replace my Marantz PM7000, which I find a bit sluggish, despite having won the best amp award in 1999. I also tested two Akais (AM35 et AM39), which were very good, with a Luxman-like sound, and a Yamaha system (C65 and M65), which was very powerful but too audiophile-oriented.
But to come back to the Teac, what surprised me right from the start was the stereo separation, I had never heard something like that!!! Superb, even though the internal design doesn't seem to favor that domain. The sound, in general, seems well-balanced, but only that. It's only after 15 minutes of warming up that the Teac AR600 reveals its qualities: Very dynamic, a physiological sound, meaning the lows and highs are quite present, which I personally like, the mids don't have that much presence, which all in all yields a very real clarity. It seems more powerful than what it's rated at. In short, a very good amp I'm not ready to let go of. Besides, I love how it looks, which is also important.
As for negative points, because there always are some: It doesn't save the settings in the memory when powered off or you have to set it in stand-by mode, but I'm being picky about it. The front panel is made of plastic, with a very nice aluminum imitation, but still...!!!
Secondhand for 150-200 euros in this category, it's unbeatable.