The PCi's are stunning I can only dream of how good the CS Ultra's are!! Dont forget they are 39" high and 16" diameter. Thats big!! My PCi 25/31 isn't exactly small. I've got it in a 15x9 room and get serious dB 16-80hz pretty much flat.
I just got a SVS 20-39 PC+ for my 14'X18' HT . I had to reduce the Subs sound level to -6 db on my receiver, and the PC+ volume to between 1/4 and 1/3. This setting makes my Sofa tremble at high Bass scenes, e.g. LOTR ... etc .
Also, the sub is HUGE. Like you I was thinking about getting a pair of these monsters. Now I am glad that I just got one. They are brilliant subs, but placing two of those in my small room would have been difficult.
My recommendation, I am not an expert, is to go with one. They are HUGE and unbelievably powerful. You can add one later if you need to.
When I contacted Tom from SVS about my Sub purchase, he recommended a PCi for my room size and listening habits. I went with the PC+ and it is excellent. You can always contact the guys at SVS with your questions, listening habits, equipment, and room layout. They will give you a recommendation in no time. You can contact them at [email protected]
Good luck. These are excellent beasts. You will be surprised at how your system sounds after fitting one of these monsters.
Ditto what everyone above has said Kain,get one see what you think,you wont be disapointed at all,tremondous power and serious bass (and I only have the 39pc+) it should pressure the size room you have very nicely if you don`t have adjoining neighbours and feel the need for more low-end then you could get another,but I have a feeling you will be grinning like a demented fool for many weeks after delivery of just one.