maybe ill put this to the test when mine comes in.
yeah I think pretty much all ipods do that cuz my ipod at max volume hooked up to the head unit aux, makes the head unit distort at 30 out of 35, if I put a CD in it distorts at 34 out of 35, I know i still need to get it tested with the DD-1 though.
Its all about signal levels, the jack on your Iphone is a headphone output not a pre-out. There is a larger voltage coming out of it, then would be found on your RCA's. So there is less headroom for your head-deck to amplify the signal, thus the lower volume before clipping.
want to understand a little more? Check this out.
