Super thanks! This is exactly the kind of non-handwavy math I have trouble coming upon myself.

It gets much more complicated with more and modern speakers doing room calibration (at least Genelec and Neumann have their own, and Sonos also has some iphone waving trueplay thing). And just saying "Niquist!" does not help to understand, e.g., how precisely can phase be aligned by applying FIR filters, and what impact does the sample rate or bit depth have.