I would skip the REL sub for now, because even with an employee discount, it's still not competitive with internet direct subs. For much less than the REL's MSRP you could get a Elemental Designs A3-250, or a Epik Legend. For a bit more you can get a Hsu Research VTF2, or a Outlaw Audio LFM-1 Plus, or Elemental Designs A3-300. Any of those will absolutely clobber the REL sub while costing much less.
+1
The percentage of cost savings off of those store brands doesn't mean anything. You'll get much better sound for LESS money from SVS/HSU/eD/Rhythmik. I have heard the REL's you speak of...(every REL sub I've heard has been depressingly mediocre for the atmospheric prices they charge). An SVS PB12 NSD (w/ the new DSP amp) or an eD A3-300 would embarrass the REL in output and extension and, due to the fact that they both have so much more headroom (and are operating squarely in their linear range), they'll have lower distortion.
The subs, price aside, are in different leagues in terms of sound quality, extension, and output.
I have a certain un-named 'box store' close to me with a section that also carries those brands and have listened a LOT to the DefTech subs. My eD A7s-450 clobbers two of them in a closed room less than half the size of my home listening room. It's better in accuracy and extension.
The guy got angry at me for running warble tones using my ipod going into the front ipod input of the demo receiver. He got pissed and asked me, "How the hell are you doing that!?" Clearly a knowledgeable salesman, he.
The DefTechs struggled to give me much output at any volume below 25Hz in
that room before they started to distort audibly and lose their composure. My A7s is flat to 25Hz at my house and is down 3-4dB at 20Hz and about 6dB at 16Hz...in a room roughly twice the size of the room at the 'box store', with a higher ceiling to boot. My A7s was cheaper than either of those DefTech subs...and we're not even talking sales tax yet. :/
There are plenty of people on this board, me included, who are confident that if you buy one of those store brands you will have buyer's remorse as soon as you hear an SVS/HSU/eD/Epik/Rhythmik.