how many ways to hook up a subwoofer

You can run a wire from the back of the Amp to the 'High level input' OR (my preferred method) go from the speaker with a short wire to the High level input.

Don't worry, the high level input just needs a tiny bit of signal and puts NO strain on the amp. The sub amp does all the heavy lifting.

@ellajeanelle    +1.

A requirement is having a subwoofer that has a 'high level input'. Connects from the output of the amp. This way it will respond to the character of the amp. If the amp is punchy you'll get that punch. If you run it from the preamp you will bypass the amp and NOT get that punch.

This was a VERY noticeable improvement in bass quality! (thanks Paul McGowen)