Ciener makes a good 22 conversion kit, but he has zero customer service. He won't take or respond to phone calls or emails. You go on line, fill out the order form, and IF you do exactly what he tells you to do, you will eventually get whatever you ordered, but that is it. He is not the kind of guy you call up or send emails just to chit chat. The Beretta factory .22 conversions kits work well, but they have gotten expensive. They turn up from time to time in the classified section of the "other" Beretta Forum and on GunBroker, but they are expensive when they do. The asking price has climbed up to over $400.00 and you can buy a Ciener kit for half of that. Since you have a 96 series pistol, it would be a great idea for you to pick up a 9mm factory upper unit. If you are going to create a "combo", it is better to use the .40 frame which has a larger feed ramp. That is what Beretta did when they made a factory combo, one frame and two upper units. You should be able to pick up a good used 9mm factory upper unit for around $200.00. Just start watching the two sources already mentioned and you might also want to check AuctionArms. Good luck.

I'm wary of the Ciener conversion. I've heard those stories about customer service, and I've also heard that they require modification to work smoothly and they don't lock open on the final round.

To do the 9mm conversion, do I need anything other than the barrel? Or is the whole slide different? I don't mind buying a spare/replacement locking block and pin for the 9mm. It'd be fantastic if I could just swap barrels to swap ammo. I think 9mm rounds even fit in the .40 magazine, right?

Finding a complete 9mm upper seems to be a little difficult. 9mm would be a great alternative to the .22LR conversion. A little more expensive, but still cheaper than .40 S&W (~$0.25/rd vs $0.29/rd).