I have a large, single, ported sub front and center, to go with my 708p. The SVS 16-PB. I think it sounds fantastic. It is annoyingly huge, but it fills in the base for movies, rock, and hip-hop. The integrated crossovers on the sub and speakers are certainly useful, but the system truly shines with a MiniDSP handling the crossover and adding in Dirac. Eyes open, I perceived directional bass with a 120hz crossover and the sub off to one side. I don't perceive that at 80hz. The sub is now centered, but I haven't played with it at different crossover frequencies. There might be a subtle impact on imagery with some music. As it is, the PB16 is capable of far more volume than the 708p can provide, let alone the 705p. If I could do it all over, I'd grab a couple sealed, smaller-footprint Rhythmik subs and use them as speaker stands. Maybe a couple E15HP2. It might be possible to go smaller and still get the full effect.