https://www.soundandvision.com/content/siriusxm-then-and-now
There were two tuners originally for factory headunits...XM tuners and Sirius tuners, and now a SiriusXM tuner. Car companies that partnered with XM originally had XM tuners, and these had much better sound quality. Sirius' signal is very compressed (much more so than XM's, and some say as much as 64kbps), has artifacts in it, and seems to have a bass boost. Anyone who's heard sat radio in, say an older Audi, Mercedes, or Chrysler product knows that the sat radio signal is much better than what is in Sirius cars, like Fords. Since the merger, most of the content/channels are Sirius survivors, and I don't know how many, if any, automaker's units still have the XM-based tuner and better signal/product.
Their streaming offerings are much better, as are the streaming services.