4-way active from a head unit requires a P99RS or a Clarion unit that is not sold new in the US. Get whatever head unit you like that has the features you need short of the DSP, and add an external DSP of your choice. There will be people who swear you have to have a high end head unit if you're going to add an 8-channel DSP, but it's not necessary. You do not need a name brand DAC to get a good pre-out signal. You do not need a copper chassis. You do not need optical out. The tune you do on the DSP is going to make a much, much bigger impact to the end result, as well as choosing good speakers and acoustically treating the car.