Following the death of my old G5 beck in the summer, i decided to replace it with a 2011 mini (lion), and had similar problems with installing the yamaha MLAN software for my sound desk.
the only option was to put Snow Leopard on it, installing from the SL disk didnt work as the installer didn't recognise the mini, so i had to do a clean install on my old Mac Book Pro with MLAN installed, then Carbon Copy Clone that install on to the mini, ( I had to boot the mini off a usb drive to format the minis internal drive) tool a little while, but worked, The Mini is stable and now Running SL with MLAN!