I have a SVS 20-39PCI. My room is the same size as yours, don't buy a new sub until you get the Sierra 2's set-up. I think that your present sub is good for your size room. The SVS 20-39 pci is a very good unit. I presently have PB13 Ultra, but I was very happy with the PCI. My PCI auto turn on stop working, and I got my PB13 Ultra at a great price, so I purchase it.
The PB13 Ultra is a next level sub, but first try the PCI with the Sierra 2's it might be enough. Boomy bass is usually caused by the sub positioning in your room, try repositioning the PCI when you get your new speakers.
1) Polk Audio
LSI 9 and matching center
2) RSL CG4 (side speakers)
3) SVS PB13 Ultra subwoofer
4)Onyko TX-SR705 receiver,Outlaw 7125 amplifier
5) Sony UBP X800 Ultra Blu-ray Player & Panasonic 55" Plasma
Last edited by alwaller; 03-21-2019 at 08:54 PM.