John is right. You are actually talking about horizontal bi-amping. if you cannot find identical amp, you will need an active crossover.
Help with vertical Bi-Amping
I have a Proton AA2120 Dual Mono amp, I really like its looks, and I like having meters on it, but I doubt I may ever come across another one, and I want to Bi-Amp my Teledyne AR-9 speakers , trouble is I cant find info on Proton to know about gsin and headroom, I want to use it on the top, and get something good for driving the bass..any ideas, or is this just a plain bad idea?...thanks Chad