Hi Jazzy,
Thanks for emailing me today. I was able to go buy another SNI-1 GLI at a local car audio shop. I tested it before I put it in the radio and confirmed it was good. Once I had it in the car, everything worked beautifully.
In fact, when connected to my iPod, amazingly the 3.5mm jack comes through with the same clean volume as the 30 pin connector on the iPod. I haven't yet tested it on my iPhone to see if I see the same results.
After my frustration of the last couple days, I'm pretty happy now.
I'll email you tomorrow regarding the details.