I've been using one for a year, with Emotiva's USP-1 preamp and UPA-1 monoblocks. Speakers are LSA-1 Signature monitors and a Salk Songsub.
It's very detailed and clear, with powerful though slightly warm bass. The bass from my Musiland Monitor 02 is tighter but much thinner, for lack of a better word. The authority just isn't there. XDA-1 highs are extended and crisp. Mids are a bit forward in my system. Tonality is good, everything sounds like it should. Upper mid and low treble has a slight glare at loud volumes and can get a bit fatiguing at loud volumes (>90 dB at listening position) to my aging ears. In my system the difference between bad recordings and good is clearly audible, but substandard tracks are still listenable. Soundstage width and depth varies with recording, but at all times image is dead center and placement is audible, if not pinpoint.
This is all when used only as a standalone DAC with volume set at max and my preamp doing volume control. I tested the unit as a preamp and through the RCA outputs it's similar, while through the balanced outs it too hot on top for my ears in my room, which isn't perfect, but is treated with 6 GIK 242 panels and 2 tri-traps with a thick 8'x11' area rug over hardwood.
I plan on trying a Schitt Statement DAC when it is released for music, but the XDA-1 will stay in the system (living room) and do duty for movies and TV, which it excels at. For music I'm looking for something just as dynamic and detailed but smoother. It's going to cost me to get it. I paid $299 for my XDA-1 on preorder from the first big shipment last year and have no regrets. For $250, I doubt if you'll find anything that comes close to the sound quality and input flexibility, let alone a remote you could club an assailant to death with, a 5 year transferable warranty and, in my experience with Emotiva, rock-solid customer service.
Definitely not the last word in DAC's, but bang-for-the-buck for sure.