how to hook up subwoofer?

Hi guys, this may be a atupid question here. There's an auction here in town today where all the stuff of a higher end audio store that closed is on sale.

I thought about getting a subwoofer if the price is right but wasn't sure how to hook it up on my 2-channel system since there's no dedicated output.

I've got a Musical Fidelity A308cr preamp and a pair of Electrocompaniet AW220 amps.

Any input would be greatly appreciated.

Thanks