i do not want to sound harsh dude. and do not take this the wrong way. my advice is to take the Delphi back. get yourself a XM-ready HU. preferrably a Pioneer, Sony, or Alpine. get the same manufacturer's XM tuner. this will be the best thing as far as sound and XM to radio compatability.
i speak from experience. i am a helicopter electrician so i have a little background on things with wires. i installed the XM modulator first. did not like the bulkiness. did not like having to tune the radio to a certain station to hear XM. did not like the static from radio going from FM to XM. especially when the volume is kinda high.
i installed the Delphi system in a co-workers vehicle. once installed the lady instantly realized it did not sound as good as mine. it was staticy. i went over all of the install to see if i had over looked something. nope. so i tried picking different stations to tune the music through. no difference.
i went back to the store where the system was purchased. i spoke to one of the salepeople who i have formed a good relationship with. i was told that was a problem with the unit's modulator. if you were to compare the Delphi modulator to Pioneer's or Sony's you will see what i am talking about.
anyway we went with the Alpine HU and XM. it was sounding real good once i got it in. no more static. now the staic i speak of sounds as if you are still listening to FM rather then XM. she was happy. i was happy. i am not happy with Delphi product however.
i have a Pinoeer HU, Pioneer XM tuner, and a Sony XM antenna. i chose the Sony antenna because it has the smallest profile of all the antennas i have seen. people will tell you the Sony will not fit Pioneer accessories. it will dude. and i am talking without cutting anything. it is just a matter of removing and installing the yellow and green clips on the wire ends. if people would just read the directions it explains how to remove/install them. it is a shame that the people i speak of are the guys that install them at some of the electronic stores.
write back if you have any questions.