I hate to bump an oldie, but I'm curious as to how this worked out for you OP. Did you go through with it and were you able to hook up the sub in any way. I'm about to purchase a modern Onkyo receiver and I wanted to continue using these wonderful Omnisat speakers. I was considering just hooking up the 5 surround speakers without a sub, but I'm interested in how that turned out for you.
If anyone else has had the same experience with this, please let us know how it went.