Check out their website to see the mix of wrecks and reef diving - the cave is spectacular: http://www.merimbuladiverslodge.com.au/ ... mbula.html
One option is to package a Sea Signs class which is underwater sign language - again see the website.
I went in Oct this year and thoroughly loved diving away from the crowds, and with our own boat (i.e. 6+ people)

Drive from Melbourne is approx 8 hours (car pool) - alternatively there's an airstrip there for those with pilot licenses etc.
Register your interest here and if there's sufficient numbers, we'll book something for next year.