I think your template demo should be installed with joomla and database Postrgresql in Quickstart installation. .
Joomla works fine in Quickstart installation with postgresql but your template and extensions not, thats the problem.
It is better remove from db requirements MSSQL and Postsgresql or explain that only Joomla is compatible with this others database types. but your products not.
Also there are not documentation or procedure to follow about joomla and joomlart or experiences about Joomla working fine with your templates and the MYSQL or postgresql databases.