Wait caus ei'm now totally confused...
UNI's css are simple includes, not css code(not classes and ids anyway).I tried copying the whole base css file contents to my file's contents (eg. common.css) but it still won't override base!
The only way i found to go on is to tweak the base css, which boonex strongly prohibits changing (and it is a good thing they say so, since future upgrades will be a piece of cake this way!)
Bout the html templates, i did both, activate my template and make the aproriate see more name change.
If you're a coder and ever worked around zen cart, oscommerce, cubecart, joomla now, that's exactly the templating system i strongly propose! (except joomla's chown prob's which are a bitch to fix after)

For now i will have to finish all the analytic part of my project that will take me months... my code might be poor, but i am of another science anyway! I'll have to show the money again :(