x2. The TH900 is the only sealed headphone I owned/heard that wasn't embarrassed by the best open flagships of today. I like it...definitely my favourite closed offering. But, it's still easily behind the HD800 (overall).
I found what were actually bloated were the transports. Using the Ref7.1 with the OR5+all upgrades, the bass was rock solid, super tight and extended beyond what I had heard previously with any converter. The bloat disappeared completely. With the MK3 JKSPDIF and other transports, yes it's there to varying degrees.
I tried the OR5 with every DAC. The Ref7.1 benefited most from it. It's sensitive to converters generally speaking. The PWD doesn't change as much with the OR5, but I still noticed an improvement, just not to the same degree as on the Ref7.1.
My Ref7.1 does not have USB (nor is it worth having). I always use an outboard converter with it. The M7 has a better USB implementation which I would get.
Listening to a Ref7.1 without a good converter really hamstrings it....
I haven't heard the Master 7, but the differences between it and the 7.1 have been described in the Master 7 thread (ie. M7 is more detailed and faster, with less bass and maybe a smaller soundstage, but more focused imaging). These are not my opinions, just what I've gathered from comparisons.
The Off-ramp 5 is a transport. It made everything I connected it to better. The OR5+7.1 is the best source I've ever heard. The OR5 cost me $2500 which was a bit out of my...
I sold my PWD MK2 for the Reference 7.1. The PWD also sounded congested and small in comparison. I'd get the Master 7 if I were you.
I owned a few Sabre DACs and they were decent for the money, but they couldn't touch what I have now. Also, I used the best computer transports with these (OR5+upgrades, MK3 JKSPDIF) since I know you brought up the concern.