just fyi, replacing the board-2.bin with the qca one is the way to go at it.
@BrainSlayer was kind enough to investigate and essentially the verdict is:
if you want 160 you have to give up the 2nd 5ghz phy. this appears to be by design.
if you want 2 5ghz phys (backhaul?) you are stuck with 80mhz.
as far as how to switch it over to 160mhz just slot in the "official" qca board-2 as @linchpin81 discovered. using the latest / recent version works fine.
theres quite a bit of discussion on the subject here up + down a few posts:
oh, also going to 160mhz you enable 8 streams on a single phy. i am unsure if this affects signal / range / etc but i would not be surprised if it did. at 2x80mhz you are getting 2 4 stream phys. ironically when i was using it i already noticed it had superior signal over for example my 301ws even in 4 stream mode, now it would probably be even better.
all that being said mine is going back in the cloest... she just runs too hot!
big hat tip to @BrainSlayer and @linchpin81 !