Hej Jonas,
until I upgraded recently I had PT 7.4 running on 10.6.8 without any problems!
"not valid audio volume..."-message:
-check that your audio volume is not a network drive
-check if your hard drive is correctly formatted (Mac OS, not: Fat32 or NTFS)
-in "Workspace" check if your hard drive is labelled as "R" (for Record drive)
Hope this helps
Hej do