Thanks for all the comments. They are helpful.
After some researching on various audio boards, I'm convinced from several comments that the 312 or MP1-C are the ticket. Looks more likely to be a pair of MP1-C's sitting in a 10 slot API rack. My current pre collection is lacking some aggressive midrange stomp, which I expect to get from the OSA. I have:
Great River MP-2
Cranesong Flamingo
Vintech 1272
Manley dual mono 40dB
1969
Ghost - which I'm selling (locally unless someone wants to drive to the west coast and pick it up!)
Ahh screw it, I'll make up my mind right here. MP1-C, here I come.
I'm not gonna like staring into the empty API slots, but that's part of the evil trick. I know I'll add to it. Besides, I can always raise my hampsters in there.

heh