As far as I know the factory XM will not work with an aftermarket radio. You should have had to buy another adapter that will need to be installed. The instructions tell you the receiver unit must be able to see the sky, just like the one on the roof. So, i put mine on the passenger side dash near the windshield and haven't had any issues. If you go to Crutchfield you can find out all that info. It's currently free with a rebate. https://www.crutchfield.com/p_220SXV...0V1-Tuner.html
The steering wheel controls were tricky to program. If I remember correctly, there are more programs available than functions on the steering wheel. I think I had to program a button even though it wasn't being used then overwrite that button later in the programming sequence. You just need to keep trying.
The date on the DIC is a known issue caused by the PAC steering wheel control module. I actually contacted PAC and they confirmed. There are other quirks related to the PAC controls as well. I just learned to live with them. The parking brake wire is only for when you want to watch dvd's. It's a safety feature so people don't watch movies and drive. I did have to ground it to the radio since i wasn't able to reset any of my bluetooth settings. For some reason that wire is related to other functions besides the brake.