I have the Polk XM Tuner
It's a really nice peice of equipment, Burr-Brown DAC's with both cable & optical digital outs and also analog outs. It also has a composite video connection so you can see what's on the XM Tuners display on your TV. It's the same size as your other components and looks good in your Rack; the Kenwood Sirrus tuner I saw was an odd looking peice of equipment but I went with XM because it's supposed to have more music where Sirrus has more Sports I believe.
I got sick of hearing so many commercials on night so I bought it, you can get it off the XM Website for $200, sells for $300 everywhere else. I paid $144 for a year of service and a one-time activation fee of $15, this activation fee has been waived for the next couple of weeks by XM - you can activate online for free now.