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.
