I wouldn't be using rec out to connect a sub as it's fixed level output (it's sends full volume signal, not attenuated by volume control) so you'll be forced to fiddle with sub's level adjustment all the time.
instead I'd choose a sub which allows you to be connected through high level outputs (through your amp's speaker outputs). subs from for instance REL or BK have this feature.
P.S. I've just checked this B&W ASW 608 and it has high level input as well so you're safe to use it with your Brio R.