Hi all, this is a bit of a weird one, but please bear with me.

I have a 2002 Lexus IS300 with an aftermarket single DIN Alpine Bluetooth/CD radio. The way the previous owner wired it up was kind of a hack job, they connected the aftermarket head unit's harness directly to the car's harness and left the chopped up factory plug in the glove box. I replaced the rear speakers 4 years ago and had to run new wire directly from the head unit to them.

As far as I know, the front speakers still go through the factory amp because if I unplug a box in the trunk, the front door speakers stop working except the tweeters. What's weird to me is that everyone always refers to the amp as the one to the right of the glove box inside the dash, but I removed that 4 years ago and my front speakers still work. Does that mean the front amp is for the rear speakers and the box in the trunk the amp for the front speakers? I also believe our front speakers are 4 Ohms if I'm not mistaken as are my aftermarket rear speakers, so the Honda/Acura radio should be good as that is also 4-8 Ohms.

I have no problems with the current setup, the rear speakers give enough sound from the built-in amp on the radio for me, no need for aftermarket amp. It's just lately I've gotten back into cassettes and have a nice deck at home for making them and want to listen to them in my car, but I also don't want to lose Bluetooth functionality.

I have space for 2 single DIN radios, so I had an idea from a project I did a few years back. I found that most Honda/Acura Radios from the 90s can drive speakers directly off the head unit, so I was thinking that I buy a cheap single DIN Honda/Acura cassette player radio from eBay or a junkyard and replace the belt inside, make sure it all works, then install it below my existing Bluetooth unit and wire it up in parallel to it. I already have the reverse harness for the proposed Honda/Acura radio and would just need to connect it up to the car.

Would this work? Leave the Alpine connected as-is, but also wire this one up the same way by tapping into the existing connections? Is there any risk of damage/harm, or interference/back-feeding of power by having 2 radios connected at once? Is there a way to wire up a switch to be able to divert between the 2 radios to keep things from blowing up?

Thanks.