1996 Suburban LS - Factory Amp or Not?

[cmcolfax]

96 LS
Non-Bose system
Front door 6.5's with tweeters in armrests
Rear door 6.5's
Rear rear headliner 4x10's

Planning new system install, but would like to use as much factory wiring harness as possible.
REALLY don't want to run more wire than what I need to hook up amp.
Head unit will power front doors, rear doors, rear headliner and sub will be powered by 5-channel amp.

Truck is not here to check RPO codes.

Per Window Sticker:
Electronically Tuned AM/FM Stereo Radio w/ Seek-Scan
Tone Select, Stereo Cassette Player, Digital Clock, Theft Deterrent and Four Speakers

Some resources I have checked imply that some of these trucks utilized an external amp.
Some refer to the small metal box under the driver's seat.

Anyone got any better info?

Thanks.

-cmc-