While I agree 1 sub is easier to intergrate than 2, in most cases 2 subs if calibrated correctly can vastly improve your inroom bass response.
Example. I have the Velodyne DD15 which replaced my Velodyne ct100e. In my room I have really only one spot for the DD15, next to the left speaker. while running the Eq I have a suckout at the listening position at around 60Hz and throwing more eq at that spot dosent really help much, so I stuck the ct100e next to the right speaker and hooked it up. What I found was having the 2 subs fixed the suckout, and walking around the room with the eq mic showed that virtually anyware in the room had a reasonably flat responce. So using 2 subs can help with the effects of room accoustics on bass.
I decided not to run the two subs simply because I didnt want the ct100e muddying up the sound of the DD15. So in the future I will seriously consider a second DD15. But I need a dedicated basement first as I have problems with the neighbours with 1 DD15
But I dont know if 2 VX-10's are better than 1 PS-1200
cheers