Just bumped into this thread and wanted to add a few things from my setup.
As well, I have a G2820 with XM and Weather, a CAMOS BTS-300 (went with that option due to the BT range), a MixIT-2 amp for the Bike (from John Brown) and the WiREVO D1000v
The hookup was easy to do, but there were a few "don'ts" that you may want to be aware.
1- The CAMOS will have to be paired with the WiREVO and NOT with the Garmin
2- WiREVO paired to the Garmin 2820 and to the CAMOS
3- WiREVO mic, plugged to the mic out on the Garmin 2820
4- WiREVO Audio plugged to the audio in on the MixIT 2
5- 2820 Audio out to the Stereo in on the MixIT 2
6- Pair Cellphone (with BT) to the Garmin 2820
Wire the MixIT 2 directly to the Bike 12v
Now you should hear XM in all his Stereo Glory! (As Larry said to me when he helped me out..)
If you have any questions, post a reply and I will try to help if you need..
There are other parts you will need like a couple of adapters and extension cables..(2.5mm amle to 3.5mm female, etc) you can lfind them for $5 at amazon from the cable store.. Let me know if you need the links.
Hope it helps and it is not to late.!
Regards and good rides!