I am planning on purchasing an aftermarket sub/amp soon, and I do plan on connecting a hi-lo converter to the factory sub for signal inputs for the amp.

My question is, can I still retain the functionality of the factory sub? Is there any issues with running both subs at the same time? My reason is, I don't always want the deep bass. So, I plan on installing a switch for the remote wire, so that I could turn off the aftermarket sub/amp at my leisure.

Thanks for any input/advice.

 

I wouldn't use the factory sub at all. Most mono or sub amps come with a remote bass/gain control which allows you to turn the sub volume up/down from the drivers seat.
Also if you use the factory sub woofer speaker wires for the input on the aftermarket amp you'll be able to control the sub woofer volume using the HU control just like you can now.

 

^ +1