Sena, or any other battery systems is great if you want to deal with charging batteries and all that stuff. I look at what manufacturers provide, and several use J&M equipment. I have a J&M system riding two up all the time. Works great. But it ain't cheap. The whole system is going to run about $1200. We use Big Ear custom molded earplugs with it. You get 30 db +/- noise protection and you get a freaking concert in the helmet. When we switched to the molded ear plugs, we turned all of the volumes more than halfway down. In fact we were able to turn it down so much, that the noise cancelling circuit became annoying. MicMutes makes a plug and play system for J&M that cuts the mic when not in use and we could further reduce the sound levels. Music is great, cell phone calls through the garmin 550 conected to teh J&M, radar detector, and FRS radio if you want it.
One thing you have is volume adjustment between you and the passenger, separate volume adjust for each of the following: CB, ipod (mp3 player), GPS, and radar. It does use cords to connect to the helmet. The mics are great and you can understand each other clearly well into triple digits.
Unlike the some of advanced digital, you are not constantly buying cords. They are expensive, but well made. I did have to send the J&M back to have a switch checked out, they rebuilt it and sent it back - no charge even though it was well out of warranty.