Well most people go full integration. Meaning for sirius get the ALP1 tuner, and the sirius to usb, and plug that in the computer. The computer will mix with GPS and send it out to the amp or in your case the HU.
You can only have 1 input at a time. So your computer must do all the work and feed your HU. Get sirius tuner for the laptop. GPS for the laptop, and if you want terrstrial radio, get the HQCT. Then you won't need the HU any more.