I'm a couple of days in with my BTR5. Nice! I don't have high-end gear, so I'll leave those comparisons to others. I can say that is sounds *really good* (technical term), particularly when playing high-quality audio files.
When connected to a computer via USB, it sounds like it could be a "real" desktop amp. Overall, the output seems drier/crisper than what comes though my O2+SCAD or Xonar STX, but is not noticeably inferior. It might actually be better for critical listening in some situations (classical). "Clear and capable" are the adjectives that spring to mind. I am sometimes amazed by how good small, wireless devices can sound these days.
I tried the balanced mode with my HD6xx and have no complaints.They sound great. (This is my first try with balanced gear, though, so I have no reference to compare.) I perceive across-the-board improvements vs. single-output mode (using same headphones). Really impressed with the BTR5/6xx combo in balanced mode. I also tried my HD560 Ovations-IIs in single-ended mode and felt there was enough power.
I spent a couple hours in single-output mode with my ie80s found myself enjoying the music but wanting better IEMs. I attribute this to the BTR5 being able to adequately drive my over-ear headphones in a way my previous mobile gear could not. The difference I rationalized as "mobile" vs. "stationary" is erased. So now the deficiencies of the ie80 are obvious.
I think the BTR5 Bluetooth detail lacks just a bit, but only occasionally. Tidal Hi-FI tracks over LDAC are lovely. I streamed FLACs via DLNA from my network using the FiiO Android app and liked that even better.
Sound quality is a *noticeable* step up up from my BTR1, which I liked when new, but always perceived as a bit muddy in the lows and artificial in the highs. The BTR5 doesn't share these weaknesses. Also, I find the signal range of the BTR5 to be much better. I can walk two rooms, often more, from my source and not lose signal. With the BTR1, I have to stay in the same room.
Usability is also good. The clip is strong and the unit is very pocketable. The buttons and features are easy to use and navigate. I haven't tried the microphones, yet.
Anyway, I'm pretty happy with my purchase so far. I keep reminding myself this was (only) a $120 purchase. I was considering buying a DAP, but this device is so versatile and enjoyable that I might not need one. I can now listen to any of my headphones/earphones wirelessly, while cooking supper or walking around the house, and have perhaps 90-percent of the experience of sitting in a chair with a wired setup. This is exactly what I wanted.