If you did not specify Rely Form URL in qDiscussionView, I assume that the the new form opened when you reply to a thread is opening the default OOB ListForm especially when you mentioned about the horizontal line that divides the message body. There is nothing Quest Web Parts can do there.
However you could create a new web part page and drop qListForm onto the page and configure it to create new discussion item or edit a discussion item. Then you just need to specify this new web part page URL in the qDiscussionView web part Reply Form URL property.