You bring up an interesting point, whether it's due to phase settings, acoustics, or placement, it does make you wonder if OP has some cancellation going on. I'm just going to reiterate an earlier point of mine: With dual SVS PB13's and a room that size, OP should be straight blasted out of his seat without those subs so much as breaking a sweat. My last setup had dual PC-13's (same driver and amp) and the results were absurd (in a good way). With them barely turned up, I had building obliterating bass. I still remember watching that intro to Edge of Tomorrow and little did I know that one should not have their volume anywhere near reference on that one. That initial bass sweep damn near gave me a heart attack. Screen was still black so wasn't expected at all. Dang near pooped myself with that level of bass.If they are out of phase they aren't going to perform well together no matter what other changes you make
OP: Your subwoofers can ABSOLUTELY hang. To the point of destroying stuff on the other side of your house if you're not careful. It's just a matter of figuring out how to make them work with your receiver, speakers, room, etc. Best of luck. You'll get it figured out. And when you do, oh man. Hold on to your hat. You're gonna love it.