I ordered one Friday. Should be installing it next time I'm home in 2 weeks. From what I see in the instructions, I highly doubt any problem with using any GPS with an audio output. Just to be sure, after I install, before I button up, I'll try with both my nuvi 750 and my iPod. I'd bet the iPod will work, just not be stereo.
If you look at the hookup you will see that you can use your GPS (with the kit installed) to listen to XM (if you have the antenna) or MP3 songs. The audio output is paralleled to the kit's trigger input on the module and the AUX input on the radio.
This is what has me thinking that the 660 & 665 GPS might generate (I do not have a scope any more to check the signal) a trigger signal of some kind just before a turn prompt is sent that the kit recognizes and triggers the radio to switch to the HFM audio input, disabling all other radio audio functions (AM, FM, CD, etc).
It almost has to because if it was just being triggered by an audio signal then it would trigger when you were listening to the XM or MP3 songs and that simply does not make sense the way it is wired into the radio.
I am more of a tech guy and at times I have a difficult time explaining myself when it comes to electronics so I hope you get my drift.
I am getting more curious by the minute.