A few brief thoughts about the HD6XX after near 60 hrs of use. I have previously owned the HD570 and currently also use the HD598. The 6XX is exclusively used in my basement system for listening to online music from TIDAL including TIDAL Masters (laptop/ DF black) but mostly for LPs via an Ariston RD40/Rega RB301/Nagaoka MP150/200 thru a Jasmine LP2.5du then to a NAD C325bee. The phones seem to be well driven by the NAD, I do not notice any lack of volumne although I listen at about 50-60 db. In comparison to the HD598s there appears to be more depth, texture and gravitas to the tunes but the 598s have a moderatley wider soundstage and seem have a tiny bit more" bounce". They aslo work well in the livingroom system consisting of a Rotel RA-1570/ CI Audio phono/Denon DL103 on a lightly tricked out Rega RB301 attached to a modestly modded Rega P3-24/PSU. All in all I prefer the 6XX and why 4 out of 5 stars...... well because I haven't heard any other phones to compare it to or thru dedicated headphone amp. Music ranges from Sydney Bechet to Miles Davis to Allison Krause to Frank Zappa Howzat!!