I just thought i'd add my experience with the Matrix Quattro for those that may be interested in using it with active monitors.
I've owned the Quattro for about a year now, and mainly use it with ATC active monitors.
I had a pair of scm50asl's, but now have some PA-65's.
I use an Arcam fmj cd33 as my cd source, and feed the Dac with with an A&B systems Black diamond coax cable. I also feed the dac with an optical cable from my satellite box, and USB from my laptop.
I use the Quattro as a pre amp into my ATC monitors using Evidence audio Lyric HG xlr cables, and have the Dacs internal jumpers at the 0db.
Before i bought the Quattro, i had an ATC CA2 pre amp.
One thing i noticed about the Quattro, was that it took a while to warm up/break in. 100hrs or so. It sounded very flat at first.
I leave the Dac on all the time to keep it warm, and have noticed that if i go on holiday and un-plug the dac for a length of time, it takes a couple of days to sound right again once its plugged back in.
Decent power cords and audio grade fuses also have a large impact on the performance of the Dac. I use a Wireworld Electra 5.2 power cord and a Hifi-Tuning Supreme3 fuse in the Dac.
I also tried a Ps Audio Ac-12 power cord on the Dac, but found the Wireworld to be better.
I don't have any other Dac experience to compare the Quattro to, only my experience using the Arcam cd33 with a passive volume control into the ATC's, and also with the CA2 pre amp.
The Matrix Quattro > ATC combination is a good one though. The resolution available is stunning. I can only imagine what a more costly Dac like a Zodiac Gold can do.
If anybody is looking for a relatively cheap Dac/pre solution for some active speakers, along with the added bonus of a decent headphone amp as described by others on Head-fi, then the Matrix Quattro is a bargain.