95-97 Premium Sound (Limited, EB) are JBL, and the head unit sends digital signals to an amplifier in the rear. All 4 channels are sent thru one wire. 98 has the amp in the radio head unit, so it is a different squirrel.
The JBL amplifier is useless for aftermarket radios.
There is also a special subwoofer driver amp which could be used.
Aftermarket stereos require a long bypass harness going from front to back to use the speakers. It is an expensive install in a shop because more trim has to be removed. The speaker harness in in the rear, and you have to take apart all the trim on the passenger side.
This is the only wiring harness that will work. It also has an antenna lead:
https://www.amazon.com/Metra-70-5601-Wiring-Harness-Bypass/dp/B0002BETAY
You CAN use the subwoofer if you can run a 12V trigger line (power antenna could be shared) to the trigger wire of the subwoofer amp. Then you can tie together two of the front line outs (not speakers) if you don't have a dedicated sub output. This will require running some extra wires with the above harness(I believe you may be able to use the power ant wire). But you definitely need 2 extra wires for the audio.
Some people also install a resistor because there is a subwoofer pop when the radio is first turned on, won't hurt anything though. I didn't have that issue, may not be a problem with these amps.