2001 Chry Concorde LXi Remote Start

The DEI systems are pretty good but I would recommend the Omega RS-4LX. It has the channel expander built in and will do everything you need for your car. In addition, it has onboard relays so that's less wiring you'll have to do (DEI remote starts are outboard). It's pretty simple to activate with your factory keyless. The RS-4LX can be setup for double pulse activation and what is typically done is, the activation wire is connected to your vehicle's door lock motor wire. Whenever you press lock twice withing 5 seconds, it'll activate. I hope this helps.

Mike

I know you don't want to replace the remotes, but........

The factory alarm system can easily be armed and disarmed by applying current, through the appropriate resistors, to the appropriate wire.  (I think it's GREEN/ orage.)

You can just buy an ordinary remote start and keyless entry unit.  Wire up the proper arm/disarm setup.  Wire up trunk pop from the aftermarket remote (just one cheap relay).

Your horn won't honk when you arm from the aftermarket remote, and you'll have no Panic button on the aftermarket remote.....but you could add that too if you wish.

All in all, going that route will be inexpensive and easy.