The CAL Audio Sigma II has a really high output voltage (obnoxiously so, in fact). One can be had very cheaply on Audiogon, and, it actually sounds darn good because of the tubed output stage. My primary DAC is a Levinson 360s, and to be honest, the CAL is, on the whole, competitive because it is so musical (especially if you use it with really good interconnects). For whatever it's worth, one of the Stereophile reviewers used one up until very recently. If you buy one, leave it on 24 hours a day (mine has been on pretty much constantly for eight years and sounds better than ever -- I've never even had to replace the tube).
Good luck