If you already have a Sirius Plug-n-play radio, then the Sirius Connect SCvDOC-1 is what you need instead of buying a new tuner such as the SCC1. The only advantage of Sirius vs XM is that you can do Instant Replay with Sirius. However, what you give up is 3 lines of data (only one with Sirius) and *no Data* on the Presets. You have to memorize whats where on presets with the Sirius whereas the XM will give you 3 lines of data, Station names on your presets, and station image-logos on all stations and categories.
I currently have both installed so that my wife and I can see which one works best, and I find the XM far more useful than the instant replay, however the Sirius seems to get consistently better reception than the XM.
If you decide on the Sirius setup, and need an SCC1, I have a new one that I never installed or activated which I will sell you for $40.... I bought it before I realized that I needed the SCVDOC and a plugnplay radio to get instant replay.
****NOTE: Not ALL plugnplay radios will do instant replay... only the Sportster 4/5 or Starmate 4/5 have worked with the function after testing it with both versions of the Stillettos.