Depends on whether it has pre-amp outputs or not. Look on the back panel.
Assuming home audio (not car) if you don't have pre-amp outputs, buy and connect a DI box like Behringer DI800 to each speaker output (the DI800 can handle 8 different input so you should only need one - about $80-$100 today). It will knock down the voltage to line level which is then appropriate for input to an external amp. Follow the instructions though if not experienced with this approach or expect gear to blow. You may need to make some cables to connect the speaker outs to the DI ins. The output will be XLR to whatever your amp takes. This unit also balances lines and removes nasty ground loop hum