no, that wouldn't work. you can't run stereo off of 1-channel...
stereo requires a left and right, or 2-channels. bridging 1-channel requires two channels, so stereo bridged requires 4-channels. make sense?
like i said, imo, your best bet is to do 150x2@4 and 600x1@4, that would require a second amp for your inboats.
you could also run, your inboats at 2-ohm (assuming 4 total) which would give you 150W to each speaker and then you could do 600x1 to the sub and buy a new amp for the 80's, something like a wetsounds Syn2 or an alpine pdx series would be my suggestion.
like i said, i think you'll be pleasantly surprised with 150W x 2 on the 80's
2003 X-2 MCX