Well for now you cannot install nethserver-php-scl following the link you gave, you need to use my repository, and of course I missed to write down the doku page
But after that I would know why you don't want to go with NS7, sure there is no more the shared folder, but you have the virtualhost solution (instead of http://yourIP/joomla, you have http://jooomla.domain.com). If I said that, I'm not so innocent, and I mean that even if the web alias is not the best solution, if you don't have it in your tools box, it will miss a day
I still think that the virtualbox panel could be enhanced by the mod_dav, the user/group authentication, some apache directives, and of course the choice of a web alias or the web virtualhost. it is christmas no ?
@davidep @giacomo what do you think
Concerning nethserver-php-scl for ns6, please let me some few days, probably I want to merge some development done for ns7
And sure, follow the advice of marc, with Centos, if you try to upgrade a version, you will merely break your system, the software collection is always the way to go.