XM Radio OR Navigation System, But Not Both
 

Spoke with a dealer today and confirmed the bad news. You can get XM radio on the non-navigation model but it is NOT available on the model with the navigation system. You have to choose one or the other.

However, as it has been mentioned in another thread, you could use an aftermarket XM converter through the AUX input on the nav stereo, or you could use an aftermarket GPS through the AUX input on the standard stereo, although neither would be as neat or convenient as a factory setup.

Seems like an odd move on Honda's part, given that they already have an XM-enabled nav system on the Civic Hybrid.