I was looking at this DAC a couple years ago while I was modding an Emotiva XDA-2. The UD-501 is a really excellently design layout (internally). It would be a very nice platform to upgrade all capacitors, voltage regulators, op amps. Stock, some people really like this. Others say it is somewhat bright/solid-state. It was originally a $900 DAC (if I remember right).
But yeah, based on what it in it internally "stock", I can totally see how the Oppo BDP-105 will blow away this Teac. Whitecamaross is selling his Oppo 105 for $699. I have heard the 105 and it really is an excellent player/DAC for this price range.
The Teac’s appear to be going for $375 to $500. It depends on your budget. The Oppo will also act as a dedicated DAC with Digital COAX or USB inputs. If I had the budget, I would vote for the Oppo. The $300 difference is more than worth it.