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I had mounted a 2-1/16" gage in that spot on my first S2000. Basically you need to gut the entire audio controller and throw away the circuit board. There is no way to do it and retain use of any of the controls. Basically just tear it apart and dremmel the opening big enough for your gage. I used the rest of the area for switches that I needed.
You could also just trash the whole audio controller and fab a whole new panel which would look better and have more options for you.