Hi Gary.
On that machine [iMac G3 600 with 1GB RAM] that is the only MIDI device attached.
OMS just has:
-IAC Driver
-Studio Patches pgm chg
-Quicktime Music
-UM-1SX
So the Kronos is NOT showing in your OMS Studio Setup? Isn't it plugged into the UM?
It might just be me but there seems to be something basically missing here.
Your OMS doc should look pretty much like this attached pic. If it doesn't, you need to fix it.
Open OMS and create a new setup doc from scratch. Uncheck modem and printer ports when it asks; Create the MIDI objects and enter the info manually. If the Kronos hasn't show up, create it by using the "New Device" menu item. Make sure you check "is a controller".
When it looks like my pic, select "Make Current" from the OMS menu and see if that works.