Hello,
The mods to my Oppo were done my Stereo Dave's Audio in Portland and involved some propriety changes to the power supply and DAC. They cost $375 and were a significant improvement. My room has two layers of sheetrock with Green Glue in between with significant absorption treatment on the walls and corners but I don't know that it would be considered "dark" Well-damped, for sure. I mentioned both Oppo's in the same sentence because they of course both have an internal DAC, are relatively low priced, and both are on Stereophile's list of Class A DAC's.
I forgot an experience i had at the CA Audio Show a few years back. I was listening to nice VSA speakers in a room that had a Bricasti CD player. The music sounded great, indeed. The exhibitor, an East Coast audio store, also had a Jolida FX Glass DAC which I was keen to hear. They set it up so they could alternate the music through the Briscasti and then the Jolida with a switch. This they did no less than a dozen times with three different recordings. Towards the end of the session, I looked at the two guys doing the demo at the back of the room and simply shrugged by shoulders because I could discern no noticeable difference in sound with either DAC. They too came to the same conclusion. The Bricasti DAC was $8500 and the Jolida, which I bought on the spot, cost $500.