Update: Since last Friday, I've had the DAC hooked up to my laptop feeding it a steady stream of WAV files for nearly 100 hrs continously.
Had a friend drop by on Sunday evening for a "test" session after about 50 hours of burn in. He brought over his netbook with JRiver and a Bladelius DAC (USB) along with his interconnects (including an Audioquest Forest USB cable). My system consisted of my Creek Evo CDP feeding my amp etc through some Ultimate cables RCA interconnects (line 1), my 10 year old Dell Inspiron running Windows Media Player, a cheap USB cable that I found in my basement storage, the SimAudio 100D, and some Radio Shack RCA interconnects (line 2), and finally my friend's netbook setup into line 3.
We used the same tracks and staggered them by 30 seconds each, so we could toggle between lines 1, 2 and 3 every 30 seconds - which basically allowed us to hear the same passage of music through each of the sources in succession - being careful to make slight adjustments for level differences.
To make a long story short, all three sources were fairly close. All 3 were virtually identical in terms of soundstaging, imaging, detail retrieval and bass resolution. While I could gladly live with any of the 3, I'd give the edge to my friend's setup which tended to have the most air around voices and intruments, followed closely by my CD player, and the Sim DAC. But of course, I was placing the latter at a great disadvantage with the setup (Window Media Player / lousy cabling). In fact, we briefly swapped out my generic USB cable for the Audioquest and it made a discernable improvement. I think the addition of a newer laptop, better media player (e.g., JRiver), decent cables, and importantly, an SPDIF/USB interface will elevate the Simaudio 100D to excellent levels - all these little things might add together for a very meaningful result. Furthermore, the DAC had about 50 hours of burn in at the time of our little test session. Hopefully the sound will continue to settle in as the hours accumulate on the unit.
I was somewhat skeptical of the whole burn in process. But I noted a considerable improvement in bass resolution from 0-50 hrs of burn in, for what it's worth. That's not my ears adjusting, since I didn't listen to the unit between 1 hour and 50 hours of burn in. The difference was very noticeable as I was able to compare identical tracks played through my CD player vs the Simaudio.
Taken together, I'm very satisfied with the DAC and look forward to adding to its capabilities in the coming weeks - I thnk I'll really like this unit.