OP, I have a 96FS and - for range use - all I do is substitute a 9mm barrel & use 9mm mags. For me it is a range gun, and I’ve run +/- 500 rounds thru it without malfunctions (that I remember). That’d be over a 4 or 5 year period. Yes, the bolt face & extractor don’t quite fit the 9mm tightly but it’s good enough to feed, fire, extract, & eject. 9mm will even work in the .40 mag for range use.
If you want to use the gun for defense - home or carry - with 9mm, replace the entire slide assembly and swap the ejector. (Somebody please correct me if there’s more). Or practice/shoot for fun w a 9mm barrel and use .40S&W for defensive use.
As to why for me, I’m a cheapskate. .40s&w used guns are cheaper than 9mm - mine was cheap enough to gat a 9mm barrel & still only have a total cost of a 9mm 92FS handgun. And 9mm is cheaper to shoot. Although folks’ memories are fading, when 9mm was hard to find +/-4 years ago, I could always find .40s&w, so there’s flexibility too.
MI2600, have fun with it!