Well, I won't need a week to figure out that this is a major improvement over the Delphi Skyfi/Sony offerings. After much thought about how to describe the differences, a good analogy came to mind:
Imagine having a CD walkman (or other portable) connected to your system as your primary CD Player, and then replacing it with a NAD 541i or similar quality CD Player. Everything just sounds better. About a 6dB increase in output (seat-of-the-pants measurement), solid, deep reaching bass, drastically improved midrange, and better treble extension. Background noise is nearly non-existant. In short, it's an extremely worthwhile upgrade if you're suffering thru XM with the Sony or Delphi radios.
The unit is light (about 5lbs) but the chasis is very rigid and the feet are better than you normally encounter on a tuner. The ability to have the menu shown on your TV is a really neat idea, and saves the eyeballs. The remote is very similar in appearance to the Delphi Skyfi, but is larger and uses Triple A's instead of the funky "watch" battery found in the Delphi. Smart. The AC cable is hardwired (no IEC socket), albeit fairly thick, and again better than the "lamp cord" you see on most tuners.
I will say, however, I prefer the orange display of the Delphi to the blue display on the Polk, but this is a purely subjective observation, and a very minor quibble at best.
Great job Polk! As far as I can tell, you've addressed all of the problems that plagued the others and brought XM to the next level. The XRt12 definitely deserves the designation "XM Reference Tuner"...Outstanding!