Bigkidz,
I've accumulated a small collection of both 12AU7's (cd player) and 6922's (preamp). In my Cary 308T cd player, I've tried Mullard's 12AU7 (nice sound, rich but a little rolled off at the top or dark sounding), RCA 5814 Black tops (Very nice tube, lack dynamics though), Telefunken 12AU7's (Great tube, all around good balance, maybe a tad bright) and finally my favorite Amperex 7316 which is a substitute for 12AU7. The Amperex has the richness of the Mullard, the clarity of the RCA, and the top to bottom dynamics of the Tele. My 2 cents....
Call Andy at Vintage Tube Services. Be patient he'll answer and he's a great guy. Very informative. If you know what you want try Brendan at Tubeworld also.