Average Frquency

I would (IF I were doing this, more on that) have the two systems on a toggle switch that could only switch one on at a time, for two reasons:  it would sound like crap with all that junk going on, and you wouldn't need to build up so much extra power capability in the alternator/wiring/etc. department.  Have two amps set up;  one for the SPL and the other for the SQ.  When you want to switch, the toggle should be on the remote-on wires behind a relay.  Switch one way, one of the systems comes on.  Switch the other way, the other system comes on.  The interior speakers would be powered from a separate amp which would power up regardless of the switch.

I asked if you were setting up some kind of a special demo vehicle because this is not the smartest way to hook up a sound system.  One good sub/mids/tweets/amplifiers/etc setup should handle all the different types of music.  You should realize that most of the difference in sub bass in the various kinds of music is already built into the recording.  You just need to build the best system you can afford and put the effort into so you can enjoy the different types merely by switching CDs.  It's a fact that most people like a variety of music types...but they don't build a different subwoofer system for each type.

Another way to change sub SPL levels, and a lot of sub amps have this built in now, is to use a remote bass level adjustment knob.  You can max it for the rap and bring it down some for country if you need to. 

https://www.the12volt.com/caraudio/theile.asp