Newb with Korg M1 trublums

[SnapChad]

I bought a 2nd hand Korg M1 about 25 years ago. I messed around with it for a while and then it went into storage. I've forgotten nearly everything I ever new and technology has changed a lot. My pre-teen son recently asked if I'd set it up for him. I cleaned it up, replaced the battery, downloaded the factory settings, connected it to an iMac via midi cable and have reset it to all the factory settings. The keyboard works great now, though a few of the buttons (prog, seq, combi) are a little sticky. Now I'm trying to figure out if it can be used as a midi controller so he can maybe use protools or even garage band on the iMac to record some things. I've got the M1 connected. It "seems" properly connected. The problem is that every time I press a key on the keyboard it seems to do something a little differently. It might give me a piano sound the first time I press. Then a mallet hit. Then a chorus sound. Then back to piano. Maybe it doesn't do anything as I press the key. I've looked at the manual and it's all Greek to me. Can anybody tell me if either (a) there's an easy fix, or (b) the Korg M1 is just too old to do what I want? Or perhaps there's something else I'm missing. Any advice appreciated. Thanks. Chad