In the US, the AR30 should be in CU mode out of the box and there should not be a problem with the unit recognising a Sirius tuner. But if, for example, a factory reset has been carried out, then the unit will power back up in EU mode. The AR30 needs to be in CU mode to work with a Sirius tuner.
To return the AR30 to CU mode, you will will need to press & hold down the BAND button on power up (at the rear mains switch) which will switch the unit to CU mode. The unit will display Region CU on power up.
Also, on factory reset the unit defaults to EU FM/AM band, which tunes in different kHz jumps to CU mode. By setting the AR30 back to CU mode as detailed above, the unit will switch back to CU FM/AM band also which will correct the tuning steps.