You might see if this helps...it is a similar post from the Apple forums:https://discussions.apple.com/thread/7041043?start=0&tstart=0
FWIW, ClamXAV is now a commercial product and is no longer free. I did not see a minimum requirements for it, so I emailed them to see if it is still compatible with 10.6.x. If/when I get a response, I will post again.
Your other option would to upgrade to at least Mac OS 10.7.x on the Mac Mini...if you can. That will certainly let you use VirusBarrier X8 from Intego (what I use...FWIW, I also sent them an email asking if they still sell a supported program for Mac OS X 10.6.x).