Okay; what wasn't clear to me before was that there was speaker wire connected to the sub to power it, rather than the low level high pass wiring, which of course can't do it.
It appears that as Matt and Rick(Wid)suggested, a single coaxial cable with RCA plugs, connected to a receiver sub out and in to one of the sub amp inputs(by convention, usually the left)would work. And yes, considering the quality of your M80s, it would seem that relatively little is added by that sub.
Incidentally, if you'd consider spending a bit more, the factory refurb X2000
here is a good deal.
