Short answer is no.

You cannot bridge ch 1 & 2 and go to 2 speakers.

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Alpine CDA-9887, TUA-T500HD, CHA-S634, CHA-1204 & KCA-410C
Pioneer TS-A6981, 6 x GM-5100T
Kicker 2 x CVR15,
MBQ RCE-216
PG MX2
Soundgate LanStar1
PAC SWI-ALP

Dude

Buy another amp. This amp obviously does not fill your needs. Be happy with what you got, listen to the correct advice you been offered or go buy something else.

Amp power to your rears when the front is only seeing 50 rms is (in my opinion) a waste of amp power. Your rears are going to be so dominant that you're going to have to turn the gains wayyyy down in order to obtain a correct front stage (or use the F/R fader control).

Have fun.