Subwoofer with BOSOZ

I am planning on building the BOSOZ. I plan on using the XLR outputs from the BOSOZ into an amp (future purchase) with XLR inputs.

I have a question regarding the use of my subwoofer (HSU VTF-2). I would like to use the RCA (SE) output of the BOSOZ to drive the subwoofer. Is this possible? I will basically be using the XLR to drive the amp and at the same time, using the RCA to drive the sub. Or would the RCA output to the sub load down the XLR output to the amp?

I do not want to use the speaker level output of the amp to drive the sub because I also use the sub for home theater. When viewing a DVD, I would disconnect the sub from the BOSOZ and use the "Sub out" of my HT receiver to drive the sub and obtain the LFE (Low Frequency Effects).