that is what i use. what i actually do to avoid the volume issue is i use the 7.1 inputs from my AVR that i use as a pre/pro. so the rca outputs go to the FL & FR AVR inputs. and since i only have 5.1 speaker setup, i send the xlr outputs with the adapters i linked above to the back surround inputs on the AVR. then the FL & FR outputs to my UPA-5 and the BSL & BSR to my dual subs
The problem is filtering the sub-80hz (or whatever crossover you choose) from the mains. Though most all subs have internal crossovers on the sub, I am struggling with how to filter the sub-crossover frequencies from the mains...I'd prefer not to have to add the XSP to achieve this..