i have a pioneer premier dehp940mp head unit.

I want to get an 5.1 dsp (alpine probably) and use the digital out of my computer. I know i can hook up my computer to the dsp with the digital out. But how would i hook up my head unit to it since the alpine dsp has only to rca in (front and rear) and my head unit has front rear and sub. Should i just leave my sub connection disconnected from my head unit?

From the dsp i can take the front rear and sub outs strait to the amps, so thats not a problem.