@ TrickyT
Great! You might also consider reinstalling directly from the Poseidon archive, just in case there are other issues lurking around - check Devs:USBHardware for case issues, too.
The Deneb didn't ship with a CD, so it looks like either whoever made it (previous owner?) used an old ISO9660 standard which doesn't support case correctly, or you're still using the CDFilesystem that came with OS3.1 which also doesn't support case correctly.
EDIT:
For your next issue, if dm9601eth.class is what the device is binding to, it's the correct class. EasyNet might be hardcoded to a limited list of drivers that dm9601eth isn't a part of. Look around the EasyNet install files to see if there's a config file somewhere that shows valid drivers, and add the new one (check the Poseidon docs to see what the name should be). Talk to AmigaKit about it if that doesn't work.
The other option is to configure the system with a different driver and then change it by hand after it's installed. I've had to do this for Envoy and Roadshow when using USB Ethernet.