SVS SB-2000 Pro/3000 vs. REL T/7x

You have posted some specifications which supposed to tell bass response. But how does it sound? Specs only tell so much. Rel adds a lot more than just bass
It will make main speakers sound bigger and better

Specs DO only tell so much.  That said these are two very well known brands.  "REL adds a lot more than just bass" including price and an extensive dealer network.  Really... what does it add?  Other posts and opinions around the internetverse that REL is more "musical" and SVS might be better in an HT system doesn't really take into account that SVS can be extensively tuned these days, has a much larger power supply and plenty of people very happy with them in their audiophile systems.  REL at this entry point into their product line has less than half the power and no room correction.  Not everyone wants to crawl around their room searching for the best sub placement.  I'm sure REL are lovely subs.  I have dual subs (other manufacturer) in my 2 channel system, and dual subs (yet another manufacturer) in my HT system.  Neither of which are REL or SVS.  And neither of which are currently available on the market.  I wish REL owners the best enjoyment of their systems.  The question stands: does an SVS sub at $799 (or $999) have a price point per performance which is at least comparable to REL's offering at $1099, which lacks the power, extension and tech that the SVS does?  And what, if any, are REL's advantages... at that price point.

I gave an answer. But you aren't looking for answers are you? Maybe someone will come along and argue with you. 

You statement of what you think it does for main speakers says essentially nothing.  

I’ve owned a few Rel subs up to the S/5 level. I currently own an SVS SB3000 and like it better. I like deep bass and this sounds great with my setup. Would I like to hear the Rel S/812? Sure.

If your amp doesn’t have the sub out (many don’t) you will need something like the Russound speaker-to-line-level adapter to make things work. Compare these you mentioned to the Rythmik F12G which doesn’t have the app that the SVS has but "might" be better. I once had both and it was close but I like the phone app.

Good luck with your search. To answer your other question Rel has- great marketing.