I added a KENWOOD double din last weekend to my 1997 LX450 and decided to keep the factory amps. I used the standard harness retro fit you can get from amazon or Best Buy with the RCA plugs. This was a super easy swap just wiring the power and grounds and plugging up the RCAs into the stereo outputs. I did hook up the “blue” wire for the antenna and it works just like the factory, going up and down when turned on /off but still having the manual switch option working. The only part that was tricky was the blue white “dashed” wire. Wasn’t a white stripe but a dash which is used to switch on the amps. I left that off the first time not knowing what it was for and not listed on the harness instructions. Once I hooked that up everything worked perfect. Only last hitch was the RCA cables are not red and white. They are random colors so you have to be careful to use them in the RT / LF. FT/BK plugs so the fade and balance work correctly. I did read somewhere here that the 1997 seemed to be the only model this worked for perfectly so I can conform that if you want a shortcut. Oh, last item. I did get a bit of alternator noise so I added ground loop isolators which fixed that for $14. Overall easy to take apart and swap.
The reason I picked the KENWOOD was for the physical volume and camera buttons. I added a backup camera and didn’t want to hassle with hooking to the reverse wire. Easer to just hit the CAM button when I need it.