Bought the wrong subwoofer!

Of course you can piggieback on the same speaker terminals. 

you can connect so volume of sub goes up and down with mains, but the best connection for my rel is with the mains at high level. the blend is seamless

A couple of notes....

The 2000 Pro sounds better and is more musical than any Rel at that price point. It is also much easier to integrate and is a very musical sub. I am not an SVS fanboy, although I do have 4 of them. Also, what is the Ops use-case? Music or HT?

If he got a 'Good Deal' on it, then he/she/it can sell it and not lose anything in the process as that sub is now close to the 1k mark. 

In my experience, the only sub that has come close to the 2000 Pro at that price point is Rythmic. However, it is much more difficult to integrate but in my opinion some of the Rythmic subs are better.

On another note, there have been a few posters on the forums who bang on about speaker level inputs being superior in every way and that is utter nonsense. We are at a point with any decent sub that proper integration can be achieved in a number of ways. There are no absolutes and anyone banging on in absolute terms should be dismissed summarily.

Of course, that is from my experience, and therefore my opinion.

If it matters to anyone, I have 1x SB 2000 Pro, 1x SB 4000 Ult. and 2x SB 16 Ult. All combined with Dynaudio Contour range in various rooms. I am in the process of selling the 4000  and switching to the Rythmic F12 because imo the 4000 is not a very musical sub and I am Music 85% and HT 15%. I am keeping the 2000 for my office which is same Ratios as above. The dual 16's I am keeping for HT duties in main system, but I am adding dual F12's for Music.

The Op has a few options at their disposal, but calling SVS will most likely yield the best results as their Customer service is exemplary. (As is Rythmic for what it is worth - Not so much for Rel).

Ken

I’ve owned three Rel subs and also own an SVS. The Rel’s have a built in line level adapter. Most Rel fans like to connect their subs off the amps speaker terminals with the speakon connector (Zu has this connection too).

You might consider buying from a local dealer and having them hook it up for you in the future

hickamore,

I can see the point of keeping full range signals to mains that go as low as yours do, makes sense, and then you simply make sure that the main amp is good for those speakers/space.

my latest kick:

Have you bought a SPL meter and measured what the speakers actually produce, at your listening position. I finally bought an inexpensive one as a tool to adjust and refine location, toe-in, and my vintage speakers have L-Pads for the mid horns and horn tweeters. 

You would learn/adjust both the mains and the subs, refining the sub’s crossover as well.

I wish I had bought one many years ago.

doesn’t need to be perfectly calibrated, just indicate SPL in relation to the adjacent frequencies. Or, if you want to know actual rather than relative numbers, calibrate it, they come with instructions.

I have several test lps and cds, I find this test cd is most helpful, among other content: 29 individually selectable frequencies, each track 1 minute long, i.e. not annoyingly short. select, see results, pause, adjust, play; next frequency, it takes a while.