I've put a 2.5 jetex system on my 850R. It has one silencer up front and nothing on the back. It's married to a 3" downpipe with sports cat.
There's no motorway drone, and once you get up above 2000 RPM everything is good. It's just a little embarrassing around town. Between about 1300rpm and 1900rpm it becomes REALLY resonant and loud. I wondered if adding one of these at the back might help:
