There are dual input speaker selector boxes out there.

You should still be able to run the iPod on the Sherwood with an iPod dock hooked up to the Sherwood's cd input; you just lose some of the controlability.

I am not familiar with XM radio as to whether or not this would also work in the same manner.

Jason
M80 v2
VP160 v3
QS8 v2
PB13 Ultra
Denon 3808
Samsung 85" Q70