Audio compression tools don't come much more powerful than xACT.
xACT stands for X Audio Compression Toolkit. It is based on a simple GUI written in AppleScript Studio and supports everything from FLAC to, Md5Sum. It can be not only be used for compression, but also for cutting and joining files such as SHN, FLAC, WAV and AIFF. You can even edit meta data in FLAC tags one by one or or in batches. Apart from compress, you can also obviously decompress between various lossless audio formats.
To process a file, simply drag it to the xACT icon in the Dock. Be warned however that xACT is quite a technical application with absolutely no help file. There doesn't seem to be any developer site either so beyond simple compression and decompression, you may have problems with it.
xACT is a very powerful audio compressor and decompressor but it can be a little difficult to work-out without any kind of user guide.
Added option to auto-create ffp file when fixing sector boundary errors and outputting to FLAC format
Fixed bug when fixing sector boundary errors and outputting to SHN format with md5.
xACT now reads album art from AIFF files.
Fixing AIFF or FLAC files now retains all of the metadata tags.
Custom tags now saved on each keystroke
Very primitive support for encoding to Opus format (lossy tab)
xACT will prevent the computer from going to sleep while there are tasks running
Review last updated: 02/01/13
Powerful audio compression features
Supports a wide range of formats
Drag and drop files into Dock icon
No developer site or help guide
Since I did the upgrade, I can't decode any files, any suggestions??? Restarted my computer, still didn't work.