Preamp into AVR?

Just bought a new home theater with the relevant parts consisting of a Marantz AV8801 AVR and ATI AT1807. One thing that did not occur to me before I bought it was the possibility of using my headphone amp, a Singlepower SDS-XLR, as a stereo preamp (I honestly forgot it even was a preamp, never having used it as such). The pickle I find myself in is that the SDS-XLR is balanced and my ATI power amp is not. Basically, the ATI only has RCA inputs, and while my SDL-XLR does have RCA preouts, there are two for each channel (it also has XLR preouts).

I've been trying to think of ways to make this work, but I have little experience in this area so could use some help. The Marantz does have two XLR inputs, and I didn't know if it was possible to go from the XLR preouts to Marantz's XLR ins to the AT.