Ncwogger,
The M24 is the next step up from the M22C. If you go to www.monarchyaudio.com you can read some reviews on it. Not that I give reviews a lot of credibility, but the one written by Lynn Olsen in PF happens to be very informative from other perspectives, in addition to the M24. It is a combined preamp/DAC, but you can run the DAC only using the DAC outputs instead of the line outputs. There is a special, it's listed on Audiogon under the tube preamp section, just do a search, or call Mr. Poon directly.
I have read about the piggy back mods for the earlier Monarchy DACs, but don't know if that is something that Mr. Poon recommends for the M24. At least he didn't mention it to me in our conversations. As for the sound of the DAC, initially I found the highs a little brittle and tinny, but after about 200 hours they smoothed out nicely. The soundstage is wide, deep, and in my system, slightly more forward. Separation of instruments is definitely noticeable and the unit, although tube based is very quiet and the bass accurate, not bloated. I swapped the stock tubes for NOS Siemens ECC88 goldpins and this improved the sound as well, although not dramatically, the stock tubes are pretty good military spec Sylvania selected by Mr. Poon. I would highly recommend trying this DAC in lieu of the M22C.