I downloaded the CZ librarian off this site for my Mac, but I can't get it to work. It says 'check midi/power connections' but I have!
The Mac runs a Yamaha CBX-T3 as a midi interface (from the printer port) then goes thru my ESi32 sampler to the CZ1000 which is set to channel 1.
Can anybody help me?

Forget that program; it's ancient, and is only a demo of C code libraries for MIDI. It probably doesn't recognise the Yamaha as an interface.

I would recommend that you buy some CZ patches from Kid Nepro. They can give you an old version of X-Or (now Unisyn) which will give you editing as well as librarian facilities. Let me know how you get on.

Now that I've thought about it...
1) Use the modem port if you can. Make sure that CZ librarian is sending to the correct port (MIDI setup?).

2) Remove the ESI from the chain, so that the MIDI i/o of the Casio is the only thing connected to the MIDI i/o of the Yamaha. The program uses handshaking; it gets acknowledgements from the Casio while transferring sysex., so it won't even start if it doesn't detect a CZ.