I just came across an Infinity subwoofer bu-1 and I'm wondering how to hook it up to a receiver that doesn't have subwoofer plugs?

Twine works beautifully. Does your receiver have analog outs?

Looks like the sub has both high level inputs ( speaker connections front right and left to the sub from the receiver and then out from your sub to the front right and left speakers) or the low level inputs...sub out from your receiver ( which sounds like you don't have )