Older docs often have more detailed info for functionality than the current docs do. And since Yamaha makes effect processors I checked those docs and found they have a goldmine of info about the various effects and their parameters.

Many of the parameters have the same names as the effects in the M but the numbers of parameters are different. And while most of the value ranges are identical there are differences there also.

But for info about what the effects do and how the different members of an effect 'family' relate and a description of the parameters and what they do the old docs have info I haven't found anywhere else.

https://usa.yamaha.com/files/download/other_assets/1/323961/spx2000_en_om_f0.pdf

That SPX2000 doc is the most current I could find so thought it might more closely match the effects in current instruments. But also check out the docs for: SPX90, SPX90II, SPX990 AND SPX1000.