Dont worry about having to turn your gain up, this does not automatically mean your amplifier is distorting more. All the gain does is adjust the sensitivity of the input stage to match the output signal voltage from the amplifier. Weaker signal voltage, higher gain setting, same output potential.
With your newer, weaker signaled h/u, so long as you aren't experiencing audible induced noise (usually a hiss or static when volume is all the way down or low), you dont need a higher signal voltage. In my experience, anything above 2volts isn't really necessary, because if you still have audible induced noise with a 2volt signal, the noise problem is big enough that you need to address it directly, rather than trying to cover it up with a higher signal voltage.
Sure, all other things being equal, Id take the 4v deck over a 2v deck. But if I found a deck that had all the bells and whistles I wanted, but was only rated at 2volts of output, Id still pull the trigger, turn my gain up, and not worry about it.
Sorry you are unhappy with your purchase. The 7949 is definitely a solid deck, I still have one kicking around here somewhere, in case I ever need it. But Id probably chose my back up Clarion deck, that's even older, before I used the Alpine.