Here is a very crude diagram of my HT room.

Any suggestions on where the best place to set a second SVS 20-39CS+ sub is greatly apreciated. I realize the final spot will highly depend on actual testing, but I am sure you can all give some good input on where would be a good place to start.

I have also been thinking about rearranging the HT room and putting my TV along the 12' wall where the door is. I have 2 extra Paradigm Atoms I could sue for a 7.1 settup, and rearranging the room lengthwise might make it better to add those in.
All Paradigm:
Fronts: Monitor 70p
Center: CC-350
Rears: Titans
Surround Backs (maybe): atoms

Is it better to have the surround back speakers or surround (side) speakers be larger?

Thanks again everyone.

You're just going to have to test in order to find the best spot. Each room will be unique. Place the sub at the prime listen location and then take readings in the locations that you think would be best for the sub. The location with the smoothest response will be where you want to put it.

And don't forget bass traps and sound treatements.

im kind of a newb,

bass traps? sound treatment? sounds expensive. please elaborate.