While it is true that you can't have both XM and the IPod interface, you CAN have XM and an auxilliary jack. I had the Vaistech SLR XM tuner installed, hooks right up to the existing amp, and had them run the aux wire to the glovebox. SAT 3 is set to AUX and the jack can be used in the headset port of any IPod, Iphon, MP3 player, laptop, etc. and play the audio over the car speakers through the existing radio. The only drawback is that you have to control the IPod from the IPod as opposed to controlling it on the navigation screen if you had the IPod interface. In my mind, a very minor inconvenience at best.....
It's not true -- I have exactly that in my '09 RX350. Dealer installed (or possibly had an autosound shop install) both XM and iPod adapter. My car has Navigation.
I had mine done at the autoshop that the Lexus dealer uses, and that is what they told me. They put the Vaistech SLR in, maybe you have the SLR2, which another poster mentioned. Wish I had known about it when I had mine installed. Do you have the IPod adapter, which lets you control the IPod from the Nav screen, or a headphone jack?