I just thought I'd list the apparently unconnected GPIO pins in case anyone else has the same problem.
My question is really though, what's the intended method to access these unused (if they really are) GPIO pins?
Soooooo..... yeah. This can be a bit difficult.
If you want to use multiple official HATs then they cannot stack by definition. There is no wiggle room due to how the EEPROM is expected to work. It seems that stacking HATs was not really something they were concerned about when creating the standard. However, if one or more of the devices do not follow this standard you could potentially stack them.
Why do I bring up two HATs? It's the cleanest and easiest solution, IMO.
What I recommend, is to try using a proto-HAT, similar to this: https://www.seeedstudio.com/Raspberry-P ... -2410.html
You can then plug a HAT on top of this, and thus be running two "HATs", the Mic Array that you want to use, and then whatever you build on the unused pins.
Alternatively, you can solder onto the exposed pins on top. This is the quickest way to achieve your goal, but messy and could destroy the HAT you have. I do not recommend this unless you have a fair bit of experience soldering. The previous method I mentioned is more organized and lets you double check your connections much easier... I am accident prone though, so maybe I'm just paranoid.
Hope this helps!