This file is a simple copy and paste ot the "Usage" section of the following link:
http://www.arnoldarts.de/drupal/?q=node/568
It contains infos that could prove useful.
 
Usage

Be sure to have a jackd running, preferable via qjackctl which also has a nice window to connect inputs and outputs like the back of your rack.

Next start jackmix. If all is well it will present you with a top-row of controls, a big matrix in the middle and some controls on the right. The top controls are the input gain, the right controls are output gain. The matrix in the middle controls the levels sent from the various inputs to the outputs.

If you are tired of the simple potis for each channel and want easier mixing into stereo busses there is help available. Just select the potis you want replaced by using "Select" from the context menu of each control and then use "Replace" in the top-left control you want replaced. If all is working JackMix will choose the biggest possible replacing control (current available controls are mono-to-mono, mono-to-stereo and stereo-to-stereo). You can fill the empty places from the "Edit"-menu.

Adding and removing of input- and output-channels is also done from the "Edit"-menu.

Please note that if no jackd is running, JackMix will start but not show any controls. You can tell JackMix to create new channels, but nothing will happen. Restart JackMix after starting jackd and go on with your work.