I received my UD-501 a few days ago, So far I am very pleased with it. I think the build quality is outstanding and sound quality is also exceptional. It did take a little bit of tinkering with foobar and using different settings to get it to play all of the different high res files but I think most of that was mistake on my part since there is not really a true how to guide that I have seen to make this particular product work with foobar. It was no fault of the teac unit. Their provided music player work fine out of the box.
First listen was through some HD280 plugged directly into the headphone output. It really brought those headphones back to life with some serious oomph compared to my computer output. I have been listening through it the past couple days with HD650 plugged into its headphone output and quite honestly I do not think it has any difficulty driving these phones. I have not yet had to turn it up past -20db. However, I do not listen to classical music. That said, When I was playing some DSD tracks which were classical I can see how you could run out of volume with these headphones. I have a Schiit Lyr lost is the mail somewhere but when (if?) it finally gets here I will be using that to power the headphones and perhaps it will reveal that they can do much more with the extra power. time will tell. But so far if I had not already bought the amp I could be perfectly happy with just using this teac to power the HD650s
One thing I will note is that if you have the DAC turned on before you boot up your computer it might cause issues. My older windows XP machine did not like it at all when I restarted and the DAC was powered on. It refused to even initialize the BIOS
