XLR/RCA Sub-Out Combo Possible?

I am running a Marantz AV8801 pre-pro in my home theater system, using Y-splitters on the dual RCA sub outputs to run four subs (3 Paradigm, 1 Earthquake Supernova). It is a 7.1 system, with two back surround speakers, and I would like to add a fifth sub adjacent to those rear speakers to fill out the bass in that area. My question is: Can I use one of the two XLR sub outputs on the 8801 to connect that fifth sub while simultaneously using the RCA outputs? The manual is not clear on this, but doesn't say that you can't do it. I have an Anthem pre-pro in a separate system which has the exact same XLR/RCA outputs, and its manual clearly states that all are active simultaneously. This leads me to believe the 8801 would also support the method of using both types at the same time, but I'm not sure. I plan to move a Paradigm Seismic 12 to the rear from its current side position and connect it to the pre-pro via a 25-foot XLR cable. Any advice/opinions from fellow bass-heads is appreciated.