After many wrong turns and much hair-pulling, here’s how I managed to upload ProTools sound files from my Mac to the Alesis ADAT HD24. Here are some notes to spare me (and possibly you?) future grief.

• Bounce desired audio from ProTools to WAV files. [I haven't tried this with AIFF.]
• For each file: import it into Audacity and export it as a WAV file. [For some reason, the ADAT HD24 doesn't recognize WAV files created by ProTools — the ftp client hangs after a few hundred bytes into the upload.]
• Rename the files as described in the HD24 manual (”TrackXX.wav” — refer to p.86 of the manual). [The ADAT HD24 doesn't recognize WAV files created by ProTools — I can't even upload them.]
• Connect the HD24 to the Mac via an ethernet hub. [I simply could not establish a direct ethernet connection, with either a direct or a crossover cable.]
• Use Fetch to upload files to the appropriate directory. [Cyberduck connects with the HD24 OK, but it displays each folder in the HD24 as empty!]