Bought the wrong subwoofer!

"Going to pick up a Rel Britannia b3."

That's a 15 year old design when the company was R E L, not "REL."

Completely different  company, with different direction.  . Part of the last lineup  when it was still  made in England.

I use 2 B3's. They do the job, but are a different animal compared to the current "REL." 

Hopefully, you are aware if it has a problem, you're SOL, as REL does not handle issues with R E L products.

for 2 channel music, don't but an SVS. The Rel is a great sub for 2-channel music, but for 1/3 the price, get a Rythmik F12G with the GR Research driver. It is very close in sound quality to the Rel S line and also has speaker level inputs.

As some have mentioned and I can attest to, SVS is not a very musical subwoofer, but it has lots of "boom boom". I sold my SVS SB1000, sounded terrible with my Monitor Audio speakers. They actually sound better, stand alone without a subwoofer for now. I do have two SVS PB1000’s in my HT setup, and truthfully, great "boom boom" from movies. Enjoy your new Rel B3 and let us know how it works out for you, cheers.

I use an SVS 2000 Pro sub with my JBL L100 Classic speakers and I have gotten them to blend really well together.  They are a very musical subwoofer if you connect it correctly and use the SVS software to control the sub.  I spent close to a month dialing it in, made many notes, trial and error and got the sound “just right” for my taste. You are blaming the sub when you made the mistake to not check out fully what your receiver has for inputs and outputs.  Don’t diss the sub for your own mistakes. 

I own a pair of REL T/7i subs and a pair of SVS 3000 Micro subs. They are similar in size, but the Micro's are a bit smaller…an eleven inch cube. The T/7i has a single front-firing 8" active driver with a 10" passive driver on the bottom while the Micro's use dual opposing 8" active drivers.

I got the Micro's because I've been waiting for ages for SVS to make a subwoofer that's designed for audiophiles with dedicated 2-channel setups instead of the home theater behemoths that dominate their product-line. I was not expecting the Micro's to give my beloved T/7i subs much competition, but after living with them for a few months, I actually prefer the sound of my system with the Micro's.

I was using the high-level inputs with the T/7i, which I prefer, but my preamp happens to have s 2nd pair of outputs that can be used for subs, so no complications with hook-up. In both cases, I'm running my main speakers full-range, but controls on the SVS enable better integration than I could achieve with the REL's.

Before this, I did try the SVS SB2000, but I could never get good integration with them for 2-channel use, so they went back. The 3000 Micro's are completely different and definitely keepers. Most reviewers who have evaluated the new T/7x and 3000 Micro prefer the former. Perhaps I would too, but in my system, the Micro's pull out ahead of the T/7i's.