I've used both PEQ's & GEQ's with good results. As of matter of fact, I'm using a graphic EQ right now. I don't think it's good to make blanket statements.... both have been used with great results for years.
The point of using an EQ is to start off with the best response possible. Meaning you equalize the response to a specific curve that pleases your ear or target curve....there are a few of these floating around the net. This means getting rid of or minimizing the effects of problem areas. I don't EQ for specific songs...I EQ my system for the best response possible by measuring before & after results.
In my experience DAC's don't make as big of a difference as a quality installation with good equipment, & good tuning skills. It's not to say that they don't, but in a moving vehicle, it will be hard to tell the difference if at all. I've used the top of the line gear from Alpine with DAC's that were used in the top gear from the 90's....from other manufacturers as well, such as Sony's top of the line Mobile ES units. A processor with four 20bit Burr Brown sine magnitude DAC's, with fiberoptic connections between the HU & processor...all digital to analog conversion happening via the PCM1702 DAC's in the processor. I've had top of line units from different manufacturers as well. All were great sounding units. I would put more emphasis on the things I've mentioned, over a DAC.