FWIW, when replacing subs in a stereo rig similar to the OP's, it was an SVS that just didn't work. I can't be absolutely sure, but I suspect it was the delay/latency from the dsp. Like the OP, I have no means to compensate upstream, and no placement flexibility. A sub without dsp worked much better, per both measurements and the ear test.
That's not a criticism of SVS, just that they may not be the most appropriate choice to integrate with an old school system that lacks upstream bass management.
