Is there an Alternative to Beat-Sonic SLA-20AD
 

Beat-Sonic SLA-20AD (Is there an alternative to this expensive adapter i want to use my Oem sub?:sad:

you can splice the wires and you will be able to adjust the sub level with the EQ on the aftermarket deck (need an HU with frequency adjustment in the 63/80Hz range). Also don't forget to remove any high pass filter on all output, or it will remove any bass to the sub since the signal required is fullrange and the crossover is already in the amp.

Basically you will need to find the wires FL,FR,RL,RR, ACC, 12V, GND, REM and Antenna in the diagram for your year. Then wire everything to the aftermarket HU, but make sure you respect the polarity for all wires.

I replaced the HU and installed an aftermarket amp under the passenger seat. I was able to reuse the OEM speaker wiring and speakers. I had to run RCA cables between the new HU and the amp and I needed a power cable run from the battery for the new amp. I did the upgrade mainly to add bluetooth and iPod interface but was pleasantly surprised at a big improvement in sound quality. The amp I used was a 5-channel Soundstream - PN5.640D. It worked perfect with the factory speakers in a '95 LS400.

IMO, the specialized proprietary interface was not worth it.