Time to face the music, I guess.
Sorry for this overly long writeup, but I think I needed to write it the way its unfolding for me.
For those with no time or patience (I feel you pain) Summary: I went from this is going back to buy this thing if your budget is under $1K. You don't have to be DSD curious, its pretty good.
So far....
First the setup: Asus notebook running Foobar v1.1.16 through Wireworld Silver Starlight to the Teac UD-50 through MIT Terminator 2.0 to Bryston BHA-1 through balanced Moon Audio Black Dragon V2 to Sennheiser HD 800 SN. 10712. Also, a Moon Audio Black Dragon balanced to single ended
The Audio drivers: for PCM Teac ASIO USB Driver v.1.02 (HS64), for DSD Foo_DSD_ASIO.
Burn in time 9 playing days, running PCM music through the USB input. I don't have a way to run SPDIF or Toslink so I can't figure out if it sounds better through there.
I listened to the Teac briefly when it came in, through the built in headphone amp, and found the sound too congested. It was actually pretty bad through the BHA-1, which is pretty brutal with bad sources, running balanced to the HD 800. It was more listenable with the AKG701.
Fast forward to six days later, and I sat down to listen to PCM music with it. I listened to a couple of familiar tracks I use for reference. I tried the CSN 24 96K 'Helplessly Hoping' for voices. I could hear that there were three singers I could place their locations, and as the ranges vary a little (I think) I could tell who was who. The quality of the bass, mids and highs were pretty good, not overly warm. I could hear the proverbial 'veiling' though, that the notes were not as clear, where the instruments dynamics were limited. I listened to a bit more, avoiding music that sounded good with anything. I listened to Weather Report's Heavy Weather, and ended up with the same results. Not as dynamic, placement was not quite what I had expected anything to sound through the BHA-1 and HD-800. This thing didn't do the detail thing well. It was slightly warmer, but not anymore detailed through the headphone amp. That I attribute to the Muses op amps on the Teac, and with a balanced to single ended converter it did sound somewhat like, the Muses.
So I let it burn in a few more days. I had a week to go before I had to return it, so nothing to lose.
Fast forward to this morning. I researched and installed the drivers to play DSD natively (thank you, Valenroy!), as that was the reason I returned the otherwise very likeable but always colored ASUS Essence One, which, for slightly more, had a very good sounding amp but did not do DSD. And everything sounded too technicolor for me. Not that there is anything wrong with that, but there are black and white like music out there that don't sound right colorized. Not awful, just not right.
I had a few DSD rips from SACDs, so I started to compare tracks. I had Billy Joel's 'The Stranger', so I compared the DSD and the converted PCM tracks. It might be the conversion, but the DSD sounded so much more alive. I checked the Dynamic Gain for both and they were at 14 (!), but for some reason the DSD sounded more like music. Everything people had said about it was true, it got louder and softer faster, and seemed to sound more natural. And from a recording people universally agree sucked, engineering wise.
But then, who lives on DSD, right? Apart from treacly obscure tunes from fringe download companies, there's not a whole lot out there. Well, I did stumble on a trove of SACD rips, and SACDs from Sony/Columbia's library must constitute some decent portion of most people's collective musical memory. Or not. But on the few I had heard and were able to compare (PCM vs DSD from SACDs) there were more subtle details, nuanced sound (the details hidden) in the music. Fleetwood Mac's 'Go Your Own Way' enchanted.
So moving on to PCM.
I revisited 'Heavy Weather', and now found that the cold had gone away. You still can't quite see between the instruments, and the recording soundstage is still pretty up front, but it was far and away a great experience. The dynamics were now there, and you can follow the breakneck pace Shorter and Zawinul dive into Havona. You get into the music, and get swept away. Very nice. I look forward to more listening.