What preamp is it? I have a Kara and run balanced out to my main speakers, and the rest of the array runs se to a block, the preamp does both xlr and se simultaneously. Depending on how far the run is to the subs, you probably won't hear a major difference between se and balanced xlr. You could probably do a miniDSP with XLR to SE to the subs which would also take care of your hpf between... I really don't know, just bumping the thread for someone smarter to chime in.