If i'm reading you right, you're looking for that 7620 tone. so...
Instead of recommending a set of dimarzio's, i can do one up on that for you- i can sell you the old dimarzio "New Seven's" that came stock with my 7620. There's still plenty of lead left on them to re-onstall them; if you'd like to check for yourself, i can get you pics. I agree, for heavy rhythm work, the things kill, and devinately put out more bass than the AN/TZ7 in there now. However, i play more lead than rhtyhm, and for me the new pickups offer more...
Anyway, pm me if you're interested.
Oh, another thing that'll help with the low-end definition; add another spring to the back of the trem cavity, and reset it up with four springs instead of three. This will put a little extra tension on the strings- you'll get a slightly "stiffer" feel, but it won't drift as much when you bend, and when you really dig into that B string, it won't vibrate at the bridge.
-Drew