OS9 is a whole different universe than OSX or iOS.
However, there is NO "class compliant" protocol before OSX.
That means, that simple magic where you just plug one of those USB/MIDI cables into the computer and it just works won't happen.
Your 61es, since it at least has a "real" MIDI out, can be made to work, but it will be a serious pain in the ass.
It will require obtaining a small old-fashioned MIDI-to-USB interface such as an M-Audio Audiophile USB.
This and a few other similar units have been known to work - sometimes. I'm not kidding… it's often a crapshoot.
Or, you can use an old standard MIDI-to-serial interface and a serial-to-USB converter such as a Keyspan USA-28X. This scheme, while known to work, now means you have two boxes and cables between the keyboard and the computer.
The Yamaha…not a prayer.
I recommend you just stick with Logic 7. All of your stuff is much newer than OS9 and the manufacturers have left the old protocols and connections behind.
Using OS9 these days requires a total commitment to a different ecosystem.
I honestly can't imagine what's in Logic 6 that's not in Logic 7 that would make it worth the aggravation.