Yes Dan, this was discussed in the thread you started 12/21/02 on Home Theater, which you might review, and your owners manual also describes the connection. In short, use one of the two cables(maybe tape the other one so it doesn't flop around)from the one sub out on the 1300 to either one(makes no difference, they join inside the sub)of the EP350 low level inputs. Since this now sends bass below about 90hz to the sub, set all speakers "small" on the 1300 and turn the EP350 crossover(not the level control!!!)all the way up to get it out of the way of the 90hz crossover the 1300 does. I'm also curious as to the speaker size and EP350 crossover settings which you've been using.
