Rodric,
First did you fix your "no sound with CD"?
http://www.avic411.com/forum/viewtopic.php?t=2632
If you aren't getting sound playing a CD, then fix that first. If everything in the Z1 works as it should, then lets move to this problem.
The IP Bus Cables are very picky about orientation and location.
Generally when you have access but no sound you have the cables in the right receptacles but they are backwards. Each cable has a blue end and a black end. The blue end goes into the Z1 and the black end goes into the first device in the black receptacle and then the blue end of the next cable goes into the blue receptacle of the first device and the black end goes into the black receptacle of the second device. Just double check the color and orientation of the cables.
Since the Sirius is between the ipod and the Z1, that might be your problem. Double check the power and ground for it. Make sure the IP bus cables are right. If that all works, try switching the ipod adapter in between the sirius and the Z1. If you then get sound, then I would agree with tillithz as the sirius module is a bad unit. Even if you haven't paid for service yet and even if you are inside a garage and get no signal, the button should be available on the Z1.