can you still change music from the ipod or do you have to do it from the stereo? and also, does it charge also?
It does charge the iPod. When you switch to another stereo mode (CD, FM, etc), it pauses the iPod & continues to charge it. You can control the iPod from the stereo controls including the steering wheel buttons. It recognizes playlists called "TOYOTA1" through "TOYOTA6" and tells the head unit they are "Disk 1" through "Disk 6." The Disk 7 setting plays all songs on the iPod...Disk 8 does the same, but in "Direct Mode" where you have to control what's playing through the iPod itself. Disk 9 is the AUX input (if you enable it).
What is the difference between this and the pa-12toy?
For my 6-disk stock stereo, I don't think there is any difference from the PA12. I think the big new capability with the PA15 was support for "NAV radios through the SAT port" (quote from the USA SPEC site). It looks like it will NOT work with the new radios that will play an MP3 CD. I'm not an expert on it though...I'd check the USA SPEC site to find your make/model/year.
will it work for the stock single disk HU?
The way I read their site, it should work as long as that HU has a "TEXT" button.
can you add Xm to this as well as an Ipod?
I'm going to do this using it's aux input. It's just a stereo RCA connection, so pretty much anything that has a line out can be connected to it. If you wanted, you could add a 1/8" stereo jack to your dash. My plan is to wire my XM line output to the PA15's aux input. I haven't done that yet though. They say all you have to do is select "Disk 9" and it'll listen to the aux input.
I drove to work & back today with it (about 2 hours total) and it seems to work well. The volume is good & the sound quality is WAY
better than an FM transmitter. I hadn't really read through the manual completely about what head unit buttons do what for the iPod control, but moving between playlists & songs withing playlists works well.