Well, I have now set up two REL Strata 3 subwoofers to my Linn Isobarik/Naim system and the results are thus:
First, it was fairly straight-forward to set them up, easier than people have suggested. Even people at REL say it can be fiddly and you can spend ages fine-tuning two subs in a system to get it spot on. It took me all of thirty minutes to get them into the right ball-park, then another thirty minutes of fine-tuning, with the help of a friend to switch and turn dials slightly while I listened, and vice-versa.
Now, at low to moderate volumes, (on Naim 72 about 9:30 to 10:30 clock position on volume dial) I have a deeper/warmer bass with a lot more 'space' and 'air' about it. The bass now has an all-new three-dymentionality to it - that was not there before. People say bass is not directional and you can't hear where it is coming from, but this is only the very lowest of frequencies, the rest you can 'place' quite easily. For me, the sound has so much more air to it now.
When I turn the volume up a little higher (about 11 o'clock) the bass has more slam and weight at the bottom. Then, as you go up with the volume, the bass from the subs and the bass from the Bricks remains perfectly balanced.
The subs bass does not overpower, or intrude at all, it simply compliments and lifts the bottom out a little, where the bricks alone do not.
Also, for classical music (Elgar's cello concerto played by Jackie), you can really 'feel' the vibration coming from that old wooden cello now, it has 'life', whereas before it sounded a little flat.
Playing Juliann Bream solo classical guitar also has differences. Yes, there are even bass notes in solo classical guitar, more space and width to the sound with a lot more 'air'. I can't quite explain this one, because if I lightly touch the bass driver in the subs while classical guitar solo is playing (even quite loud) the bass unit is not moving at all, I can only detect the slightest electrical current coming though it, yet, there is now more detail coming through and my system is a little more revealing than before.
So, my two REL Strata 3 subwoofers cost me £225 each, off eBay. I had two 3meter leads made up to come out of the Naim hi-cap. The results, Thank You very much, I'm thrilled,
Oh, I also have two nice large wooden objects to put two big plants on now