Looking into aftermarket head units and don't understand the difference between 2 and 4 volt preamp outputs. Does it matter?

Will be running the Hawg Wired 300watt (4x75) amp with 2 6.5" and 2 6x9's.

Looking at the Sony digital media receivers.

 

It means that the 4 volt output will drive the amp more efficiently. Unless you have an amplifier with really low input sensitivity, it really shouldn't matter. You will just achieve the same volume at a lower setting with the 4 volt unit. Either one should drive the amp to clipping sufficiently.

Shakey