My Alpine HU has most of the usable DSP features that I need with the exception of flexible crossovers...The HU has time correction, graphic and parametric EQ and plenty of channels of output plus subwoofer level control. The only thing lacking is bandpass capability on the crossovers...so i'll be using the Dayton DSP strictly as a crossover and all other processing will be via the Alpine HU.
The DSP-408 is a nice little unit and it's pretty inexpensive...It does have it's limitations though and it's lack of dedicated subwoofer level control *****, but there are many amps that offer that feature, it can easily be worked around. Unfortunately i have yet to install my new system so i can't speak to the SQ of the unit.
Oh...random insult to forum member showing how cool I am.