Update - Got it working, I had to modify the server name in db.properties file (..\epo\server\conf\orion) folder to be the servername rather than 'localhost'.
The error log in %temp%\mcafeelogs pointed me in the right direction with the following line:
20131021153107 Server names DO NOT MATCH so block the install. Servername from SQL server : [EPSRV1\EPOSERVER] Servername from installer : [LOCALHOST\EPOSERVER]
Setup then continued as expected.