Hello Mdrew,
Hope you are well. I have an H/K AVR 630, there is always a pre-out signal even with the speakers connected on my unit. I would assume it is the same with your 7200. I tested this with my speakers connected and ran the pre-out to an old receiver and the signal comes through fine.
As far as why the pre-out is cleaner, it is not amplified yet. When you run the speaker cable output it is amplified by the receiver and then amplified again by the subwoofer amplifier this can distort the sound, compared to just amplifying the signal once.
The SVS PC-Ultra with the parametric EQ has a 525watt BASH amp, it will easily handle your room and much more. You might not even have to put it downstairs with your speakers therefore eliminating such a long cable run. If I remember correctly your HT is on an open balcony, yes? Try putting the sub at the rail and see how it sounds with your mains downstairs. Another benefit of this is you could quickly unplug the downstairs cable, and hook up your HT cables and use the Sub for both areas with a slight adjustment of the subs volume.
As far as downfiring subwoofers is concerned people seem to prefer the downfiring models. I could not find any specifics on this topic. Biggest reason I can think of is the dispersion of sound is 360 degrees with a downfiring model, which would be very beneficial if you try the sub in the configuration is suggested. Plus the driver is indeed protected from poking kicking etc....
Later,
TonyM
