My dealer told me the same thing, that you could have the VAIS Tech iPod adapter and XM. However with the Lexus iPod adapter you could only have iPod and not XM.Well I'm not sure how but on my 08 I have both. The XM adaptor was already installed in the car when I purchased and I had the dealer install the Vias ipod and they both work just fine. I have no idea how it hooks together though as I've never looked, but it is possible to have both.
The factory unit goes through the AUX input, IIRC. My VAIS Tech unit goes through the CD Changer input. Hitting the CD button multiple times cycles through the changer and then the iPod.
My VAIS Tech unit has been a bit flaky, so if you aren't wanting XM, I'd go with the factory unit.
08 Smoky Granite Mica IS-F