Good luck on that.
You do not get something for nothing. The only way I can see to do this is using an external amplifier. Switch line level signals from the scanners and output via FM or BlueTooth to your stereo system. Otherwise you are taxing the hell out of the barely adequate audio amplifiers built into scanners.
I found 1.6 volt LED and they work PERFECTLY, I was using 3.2 V, To High
I am NOT using the audio amp of the scanner.
I figured it out and anyone can that takes the time to actually sit down and do it, instead of thinking about all the reasons it Can't be done....Because It CAN, There is such a thing as over analizing and that is most of time the issue around here, alway's why it Won't work, Never trying it, just saying it won't seems to satify most, well that's not how I approach it, get in there and play around and MAYBE, Just MAYBE, You figure it out and when you do, You get to pat yourself on the back, or you can just say, Told You So........
It works.....Very simple, It Works.
1 LED Bulb 1.6V and two jumpers, DONE.......Mission Accomplished.