If you grab the signal before the amp, it should be dead ruler flat with no processing whatsoever. It's the amp that applies all of the BS. This will negate the need for the Fix 86.
When I measured the output of the Bose HU in my Mazda3, this was exactly the case. I don't have the Bose in my CX-5, so I can't really say with 100% certainty this is still the case, but that's my suspicion.
Before you spend all of that money on the Fix, I would measure the HU output before the amp with an RTA and confirm this is still accurate information.
You can make your own RTA with the help of this video.
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