I have just finished this setup and will leave on a 3200 mile trip tomorrow.
I had power for the Zumo 550 installed to the left handlebar. After much head scratching, I installed the Zumo to the BMW cupholder. Stuck velcro to the upper cupholder strut and ball mount (to prevent sliding), then wrapped two plastic ties around both. I positioned the Zumo in front of the volume/tune button, thereby getting it as close to my left hand as possible. It turned out better than I could imagine. It's very stable. (To illustrate how happy I am with the Zumo; my chief complaint is that the security screw locks itself during a ride of any length. Vibration and gravity. I can remove the screw completely, but just where do I store a micro-sized screw and remember where I put it three months later?)
Power and antenna to my Inno XM Sat Radio goes into the center compartment. I affixed the Inno mount on top of the compartment with velcro and connected the wires. I also put a little velcro between the Inno and it's mount. It's not going anywhere. I've got it positioned so that when I park the bike and lock the wheel, the XM is sort of hidden under the handlebar. If (when) I forget to take it with me, the chances of theft is reduced.
I purchased the Cardo FM version. I listen to the XM radio via FM, and receive GPS and cell phone via bluetooth. It all works just as intended. The quality of the speakers is very good. I've got a flip up helmet, which is as loud as they say it is, but I can still hear the music, GPS, and phone with no real trouble, all the more impressive because I have 60% hearing loss in one ear. Placing the speakers properly in the helmet is key. A half inch can have a big effect. The volume control of the Cardo doesn't allow as much fine tuning as I'd like (too loud or too quiet), but that's a minor problem. Music via bluetooth is still bad, so I downloaded an audio book to the Zumo. I'm better set up for entertainment on the bike than in my house.
When I finally get my SO to join in rides (not if, but when), my theory is to get another Cardo FM. She'll be able to hear the XM radio or find a local radio station. If she wants to talk to me, she can just call me on her cell! Unlimited minutes. Frankly, she has this habit of yelling "Watch Out!"
when I drive. I'd just as soon not hear it via an intercom.