Beginner question re: which rca outs to use for active system

[will5023]

My head unit (Kenwood KDC-BT372U) has 3 sets of preamp outs - front, rear, and sub.
If I install a multi-channel dsp/amp for the front and rear speakers and a separate mono amp for the sub (using the processor to tune, then sending preamp output to the sub amp), would I use only the front pre-outs on the h/u? Or fronts, rears, and sub pre-outs and combine them in the DSP? My head unit has bass controls (bass level and bass boost, iirc), but would i need these if I'm using a DSP?
Related question - if I end up utilizing the bass controls on my h/u, would I need to use the amp's remote?

EDIT: added "dsp/"

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[ThxOne Premium Member]

I am a Kenwood user... my advice. Use all of the head units outputs into the DSP. If you use your BT for calls and you do NOT use all of the outputs on the headunit, you may not heat the caller very well. This is currently my issue and I will be hooking up all of my head units outputs to my DSP soon. To use the bass controls (sub control) you will want to use the sub outs on the head unit into the DSP.

 

[ThxOne Premium Member]

Oh, if you are using a DSP... you don't really need any of the on board kenwood enhancements like bass boost or loudness and so on.