three set of pre-amp outputs for tri-amping?

Is it possible to jumper the tape input/outputs to convert one pair of the four RCA jacks for driving a third amplifier for tri-amping? Or do I need to have a third set install and wired internally?
Tape outputs are a fixed volume so they will not work. You might be able to wire in another pair but I would think that the output will be compromised and level sets will be different between all three outputs if two are bridged together.

If you are triamping you should be using an active crossover driven from your preamp or a DEQX system or something similar