Also XM is not sync up like Sirius so if you have 2 xm's side by side they will have a huge delay.
I've got XM in my boat and another boat tied up with us and on the same channel it sounded like the old days of a concert arena surround. The echo was something else, even from one boat away. It would catch up a bit and get pretty close but they were never dead on.
I've got Sirrius in my truck, and as previously stated XM in the boat. I hardly listen to the XM in the boat as we tried it last season and it was the same 4 songs over and over on channel 20 or whatever the hits part of XM is. On the flip side, I've tried to listen to Stern on Sirrius when I'm in my truck and I just find him boring any more. I do dig the Hits 1, 80's 8, 90's 9, 20 thru the 23 hair nation channels. Much more music and variety.
Then again, my company truck only has terrestial and I spend most my time on Frosty, Heidi, and Frank and then Leykis.