I get the same error during install.
I tried in one server and got the error "To install the Docebo suite you must have the domxml module installed", so I tried in a different server and was able to get to step 7, where I got the error :
Warning: Unable to set property: nodeRef in /hsphere/local/home/username/mycollege.com/install/lib/lib.domxml4.php on line 272
Fatal error: Call to a member function on a non-object in /hsphere/local/home/username/mycollege.com/install/lib/lib.domxml4.php on line 657
So my conclusion is that the problem in not the domxml.
I am getting frustrated as I tried in 3 different Linux Red Hat shared servers and still have not been able to install.
Is there a workaround this problem or maybe a manual install ?