I've heard them, and they are two VERY different animals. The DR-6 is a great SS preamp, IMHO. Warm, sweet, as close to tubelike as SS gets. The Adcom is more detailed and extended, though a bit sterile sounding for my tastes. So it would depend on which direction you wish to go in, as their sonic signatures head in opposite directions.
Cheers,
John
Cheers,
John