I downloaded the system dbase, then upgraded to 6.0.11 without issues. What I want to do is restore the mailboxes and audiotex files I successfully saved on usb stick. Is it possible to restore 6.0 voice mailboxes and audiotex files saved using 2.3 backup to the upgraded 6.0.11 system?
Not sure about that, normally you have to go 4.0 first, then up to 6.0...
Assuming you have the correct license, I would convert the database with the DB Convert tool and restore it... this will restore mailboxes, greetings and audiotex recordings, they are part of the database not the VM backup. Messages are stored in the VM backup.
I don't think upgrading directly to 6.0 is supported from 2.3 though, the db convert tool may fail. The release notes are very clear about how this is done because the core Linux files need to be upgraded separately from the call processing software, you must have a minumum 1GB CF card and then upgrade to 4.0, then upgrade to 6.0.
Are you a certified technician?