Hi,
I own an iRig HD2 and I think it's a great device! Just recently I also wanted to be able to record vocals and to charge my iPhone while working with Amplitube. So, I bought the iRig Pro I/O with the power supply. It works as expected, just the manual should state that it will only work when batteries are inserted or a power supply is connected when working with an iPhone, IMHO.
Now, when I record guitar or vocals, I notice that the recording volume is very low. Of course, I set the gain settings correctly, but the output signal going into the phone, which is recorded, is very low and I can't seem to adjust it. Only when I normalize my recording, the signal will be normal (as in three times as loud as when it was recorded). I was wondering if this is my iRig Pro I/O that is damaged, if this can be fixed with new firmware or that this is normal? I don't have this issue with my iRig HD2.