REL505 vs SVS 2xSB13 or 1 x PB13

My home theater system consists of Integra DTR9.9 integrated, PSB synchrony 1 fronts, PSB B6 surrounds and a REL R505 sub. My room is about 20'x30' with vaulted ceilings and opens to the kitchen. I use the system for blu ray/dvd music video's, regular CD's and cable, pretty much in that order.

I'm thinking of upgrading my REL to either 2 SB13's or 1 PB13 from SVS. I'm pretty certain that the 2 PB13's will outperform the REL, but will they outperform the PB13? Which would be more musical? On the SVS website the specs indicate that the PB13 digs deeper into the lower octave than the SB13, which may be nice for the deepest organ notes. In this price range are there any other subs that I should consider?

Rythmik F15HP (sealed) or FV15HP (ported).
Thanks BDP I'll check out the Rythmik site.

I think what I may try is to continue with the REL to augment the lower frequencies of my PSB mains, using the high level speaker connection but no LFE connect. Then use the new sub, such as SVS SB13 for LFE effects. I think my Integra can handle this type of setup, if I can't get the two subs to integrate good enough, I may then spring for a second sealed sub.

what don't you enjoy about the REL sub?
To my ears, these are the best in the marketplace.
Very musical and so easy to integrate into any system/room.

Keep me posted & Happy Listening!
Jafant, there is really nothing about the REL that I dislike, in fact for music it's really good. It will literally rattle the eyes on certain tracks. For LFE in my large listening room I think it may be marginal at best. So I think what I may do is keep the REL hooked up to the amp speaker terminals, then try a SB13 for LFE. Or something like that. If I could find a second hand R505 I would buy it, but they come up only rarely.
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Denver craigs has a pair of SVS PB13 Ultras for sale... No affiliation
Sorry, that was supposed to be a private message; my mistake