Those aren't Delco, or Bose, or any factory rear speaker. Those are aftermarket. And if you don't have a "Bose blah blah" nameplate show-off plaque under your radio then you don't have bose. The gain slider was only included with the premuim amplified system from GM. Also, u do have it because you have 4 wires going to the raer speakers, which is a definate sign of the amplified system, because of the DVC rears gm used. If you had the Bose, you would only have a pair of wires (like you have) with an adaptor for the wiring harness (more or less like you have). The Bose speakers in GM'* always for some reason used spade plugs like regular speakers that went to an adaptor so GM could use them.
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