i downloaded your Quick Cart versión. (loaded 1,4 flat) and is a very good work. I installed it in my local server for test and was all correct except one thing.
When i activated the taxAndDiscount plugin all is correct before make the pay, but if i activated the htmlMailOrderDetails plugin, the email sending to the clients dont have the tax and discounts shows.
I don't think there is a way to help you. It seems MailOrderDetails doesn't support tax and discounts from some other plugin. That is some work for someone you pay, or perhaps for you, if you know how to code.
