Tough call. I’m in the same boat. There are lots of synth books but none of them seem that appealing. I might add another $41 so I can get one of these and tune my monitors: https://www.amazon.com/dp/B00N4Q25R8

mesurement microphones are the answer, cheapest/simplest is this here https://www.amazon.com/gp/product/B00N4Q25R8/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=B00N4Q25R8&linkCode=undefined&tag=roomeqwizar07-20&linkId=11cec2339d26c67de40e894f38f2fbd7

For top of the line pro level stuff, look at Equipment from Bruel&Kjaer