Which REL sub, R528 or B2

I rest my case.

Xti16, what crossover frequency have you set up with C1? How big is your room?

My room is 26 1/2 ft X 12 1/2 ft with the speakers on the long wall. It's the only way my room allows. Anyhow I have the B3 crossed over at 33hz. The sub sits about 3ft to the right of my right speaker. For me I want to have the sub pick up where the C1's leave off. That being said I only have a few recordings that go below what the C1's are capable of. But the sub adds just a hair of weight to the mids also. Again if a Rel is in your future and you are going to use the high level input consider an aftermarket cable.

BTW is are your C1's the original or MKII/Sig? I upgraded from the original to the Sig in Mocha and have only the rear post (stand4) filled with sand about 3/4 full. The MKII/Sig sound a lot better at lower listening levels.

My C1 is the original one, stands are filled with sand, actually "cats" sand, both posts filled. I've read good things about MKII. Better clarity and better at low level listening as you said.
33 hz makes perfect sense, I've seen frequency response to crossover plot of B2, quite interesting. The output doesn't prgressively extend towards higher frequencies when you change crossover setting but it acts more like tilt control.
You have kind of "Audio Physic" setup. They recommend speakers on the long wall. Your sub is not in the corner then, how far is it from the wall? the front wall I mean, not the side wall?
I've ordered a REL, and have some expectations...

Xti16, one more question, have you tried the SignalCable subwoofer cable?