I too have the XM system in my TT and Sirus in my truck and have looked for a docking station and receiver to replace the XM in my TT. No luck yet. To be honest I haven't searched very hard because I have been using the music stations available on my Dish or Pandora.
If I find a Sirius setup for the TT I will post it here Cowpaddy. Good luck.
As an aside, I let my Sirius subscription expire and waited for them to contact me. On their third attempt I told them that if they would renew me at 50% off and waive any fees I would sign up. They did!
Steve & Lauren
2011 Windjammer 3065W
2012 Ram 3500, 6.7 Cummins