If your are unhappy with the hardware replacement offer why not ask for your money back plus accrued interest, and lost productivity compensation.
That total should be well above the cost of an 8-core mac. Apple should do the right thing here, look how many problems he's had with this. Its insane, its crazy, it deserves to be made right.
That being said, the cust. service agent on the end of the phone, probably has no authority to do what would be, in my opinion, necessary in rectify this extremely crazy scenario. You'd need to get to his bosses boss, someone with authority to say "holy bleep this guys been through the bleeping ringer, we gotta make this right."
If it were me, I'd ask for the cash compensation as detailed above or the octomac and if neither of those work then I'd let them know I'm considering finding a lawyer to get involved in this crazy mess, with the disclaimer that you really don't want to do that and all you really want is to be a happy customer of Apple's.