My main question is: does it matter what position each component is hooked up on the bus? ie: does the i-POD interface have to go into the XM reciever or can it be hooked up the other way around?
It doesn't matter the order. It only matters which colored end of the cable goes in the correct way. IP Bus cables can only go one way, there is a "towards the Z1" side and an "away from the z1" side. Keep the orientation correct and the actual order of the devices doesn't matter.
That said it only matters unless you get the "cheap" AUX input
http://www.crutchfield.com/S-GcceazDvQR ... =130CDRB10
which needs to be the last in the line. I also believe that the CD changer needs to be last in the line, and if you have a cd changer, you can't use the "cheap" aux input and you would need a more expensive aux input
http://www.crutchfield.com/S-GcceazDvQR ... =130CDRB20
if you wanted aux and cd changer. This expensive aux input can go anywhere in the line and the cd changer would need to be at the end.