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.
