Sunn Model T head. Not sure what he uses for distortion, but he uses a DL4 for all the looping. The thing I really like about Russian Circles is, whenever you hear 2 guitar parts it's because he just looped something on the fly. They're a 3 piece only, but his clever use of looping helps fill out the sound dramatically. The drummer is super tight too, to be able to keep perfect time with the loops.
I just caught a thread on HC about this and someone posted a decent link.
He is using a Sunn Model T reissue (clean channel only) and if I remember right an ocd and a ts also he is using a headrush now for the looping.