From the top of my head:
- Attach your Amiga hdd to your Mac's IDE bus.
- Start UAE, mount a local directory as dh0:
- Mount the Amiga hdd as dh1: or something
- Download whatever you want from MacOS to the local directory mounted as dh0:, then copy it to dh1: from UAE
- Reconnect the drive in your Amiga.
[Note: I've never done this myself]
