Do the units come with preamp RCA line-outs for hooking up aftermarket amps?

Yes, but keep reading.

The included RCAs provide UNPROCESSED, unamplified signals to aftermarket amplifiers.  This means that the volume would no longer be controlled by your volume knob, you'd need to have an external signal processor, EQ, crossover, and/or separate volume knob for your amp(s).  

AuCar has stopped including the RCAs in their kit for this reason.  

However, I'm aware that some of you have high-end audio systems with external signal processors, so I'm including the RCA preouts in all kits purchased from squarewheelsauto.com.   

My recommendation is still to install your amp and subwoofer this way:

This setup has been working great for me and hundreds of other customers.