If you have the space on your amiga HD, I would suggest using ABackup from Aminet. It is shareware, but there are no limitations on the demo version. From there you can create an archive of your amiga and save it as a single file that you can then FTP to your mac. That's how I do it and it works great.
At least on the latest version of lha, the docs states that archiving more than 2GB will "confuse" lha. And I'm pretty certain that SMB cannot handle files larger than 2GB anyway.
