I don't have a modular helmet, but I just curl the Parrot mic up under the chin peice and tuck it up next to the left cheek pad. Folks I've talked to while using the Parrot can't tell I'm on the bike. There's a little background noise but not enough for them not to clearly understand me.
I bought a little A2Dp Bluetooth dongle from http://www.cubeternet.com
that i plug into the audio output of my 2820. I then set the audio on the Garmin to headphones. I now get my XM (or MP3 in your case) AND the Garmin voice prompts via stereo in my headset. The downside to the dongle I have is that is only lasts for about 2 - 2.5 hrs. I can recharge it on the bike using a USB car charger, but that takes about an hr or so. If you want to go this route, look for a dongle that will last a little longer.
I like the way the V-Can has everything built in. It's a nice clean setup, but I personally like the flexibility of being able to move the headset to a different helmet if I want to.
BTW, I have my iPhone and the dongle thats plugged into the 2820 both paired to my Parrot. The Garmin functions as normal by interrrupting the music to give me commands, and if I receive a phone call, it is announced as " Call from Dick". I can then say "Accept" to take the call or "Cancel" and hang up on him. But Dick is such a nice guy I would never hang up on him! The music stops until after the phone call, then resumes.
The handlebar remote will control the volume and allows you cycle through Bluetooth audio, telephone, or radio - announcing each one. It will not control your MP3 player, ie, you can't skip tracks or pause. The 2 buttons on the remote only control the radio to allow station surfing. So, the remote has 5 buttons: 2 for vol, 2 to select radio stations, and 1 to change functions. If you want to place a call, you MUST cycle through the functions to get to telephone, then press a button to place a call. It will ask "Who do you want to call?". Wait for the beep and simply say, "Dick cell" and off it goes.
There are lots of good choices out there now. Good luck whichever way you decide to go.