Amazing. I went through the exact same thing last night on my 2004
MCS with h/k. I was sitting in the garage for about 30 minutes trying to figure it out. My wife thought I was nuts. I kept looking at the manual at the "SPEED VOL" instructions but couldn't find the feature on the stereo. I'm glad I didn't even have to bother searching this forum for the answer, it was right at the top!
-GothamTaffer