Yeah it works fine Lee, just plug them into the main analogue outs.
Or you can buy a couple a phono coupler and run a sub with the speakers direct, you don't need a processor if running 2 channel.
I ran them with the 568, DSP33C and a Rel sub recently for a few weeks and it was good, set the crossover to 80Hz and they start to really sing at all levels.
Are you talking about Beolab speakers here?
The 6000s will run on "line-in" RCS, like you say.
But beware if you use them for rear surround (as I do) !!
The rca is "signal sensing" and due to the rear not normally being on all the time on surround soundtracks they turn off.
The only problem is there is a delay when they turn back on that can ruin the effect ...
I have a complete Beolab 5.3 system and use converting cables from RCA and 12v trigger out on my processor, to Beolink plug with 5v trigger-in for the speakers.
That way they turn on with the TV/DVD/processor, and more importantly don't turn off until I turn off one of the above.
Hence the "headache" thing in my sig

I've been with B&O for few years now, and from a design point-of-view they're quite excellent.
True story :
I once bought a Meridian 7.2 system and when I told my (designer) girlfriend what I'd done she asked to see a picture.
"Where are you going to put that? In the garage ? " she said before walking off.
I still have B&O ...

The Beolab8000 sounds much better than the 6000.
The 4000 are real good speakers and a good alternative to both the above.
Sound better than the 6000 and easier to place too.
I had a pair in the "listening room" before I replaced them with 8000s, and I'm tempted to go back to them ...
All have problems with deteriorating rubber surrounds on the drivers, but it's cheap enough to repair or replace.