Easy answer? Get a new deck.

I imagine you want to run bass of one amp, speakers off another?

A deck with multiple pre-outs is going to give you useful features like independ sub control (bass up/down), allow you to adjust fade/balance, crossover/EQ settings, etc.

Some amps do support a pass-through feature that allows you to plug one amp directly into another, but I would honestly only use this myself if I was running the same sort of speaker on the other amp (e.g. 2 subs, 1 amp per sub).