You need to apply some changes which were introduced with version 6, but you can directly install version 8 (or 9 - depending from what you expect performance-wise) - no need to install version 6 or 7:
- clean all parts, in particular the fans
- check that the early ECNs have been performed (e.g.
ECN-0188 Pearl Expert Touch Wing LED flicker, and
ECN-0191 Dongle Connection Point Change)
- disconnect CD drive
- replace SATA cable with a lockable one
- I'd also advise, since the console must be somewhat older, to check the BIOS battery - or maybe just replace it with a new one
- update BIOS, and apply
the correct settings- update harddrive firmware (if applicable), or
- change harddrive to be an SSD
- extend memory to be 4 GB
- now install version 9 (or 8 ), followed by 9.1 (or 8.1)
- update USB panel firmware
- apply for a licence, import licence
- update personalities
The 'version 6 changes' are listed here:
http://www.avolites.com/software/downlo ... v6-upgradeI'd say that's it

- you might be in touch with Avolites or your Avo distributor in case of questions