I will add that the most well known firm, Audyssey, is rather coy about exactly how many filters are technically available in products they license -- https://audyssey.zendesk.com/hc/en-us/articles/212347743

Quote:
The filter resolution depends on the processor in the AVR. It is where the filters have to run ultimately and so they will be XT or XT32 depending on which AVR you have.


Once upon a time they did offer stand-alone eq -- https://www.avforums.com/review/audyssey-multeq-xt-pro-sound-equalizer-review.2