So are there any pitfalls to watch out for if I want to hook-up both of my subwoofers, to BOTH of my systems? I was wondering if there could be subwoofer damage if both systems happened to be on at the same time, and maybe they both sent conflicting signals and caused something "bad" to happen or something.

My computer is pretty much in the same room as my HT- it's in the adjoining dining room, but essentially it's the same room.

Actually it would work best in my system(s) if I used both of them for the HT, and one of them for the computer, so I'll do that if there isn't any issues to watch out for. Maybe I'll move my STF-2 to the side of the room with my computer, and put my new one where my STF-2 is now, and use the STF-2 for the computer subwoofer, and both of them for the HT. Is this reasonable?