direct input of Nemeth in Duxbury

The simplest way to do what you are asking is to open a separate DXB and six-key your braille in that document. Once you have brailled what you desire, then you copy that and insert it into your DXP within the codes [cz] and [tx], which begin and end exact braille translation where ASCII input is translated to braille output. These can be inserted via the keyboard shortcut F9; just type the first code, hit enter, press F9 again, type the second code, and hit enter. You can use the <ExactTranslation> style, but directly using the codes sometimes works better than working with a style, especially with more complex constructions.

If you know the ASCII equivalent for your desired symbols, then you can just type those within the [cz] and [tx] codes without having to six-key your braille.

Also, modified expressions can be inserted in your document using codes, which cuts out the hassle of six-keying your braille. For your example of the modified sigma, the code string would be [e]σ[bar], which would give you a sigma with a bar over it. [e] signifies that what follows is a modified expression; the sigma was inserted from Layout: Code List menu, or keyboard shortcut F5; and [bar] inserts the bar above in this instance. All of these codes mentioned in this post can be found within the Layout: Code List menu and are explained within Duxbury's DBT Code Quick Reference article found within the Help menu.

Please forgive the length of this response, but I thought I would give you a couple of options to explore and consider when inputting mathematical/technical materials in Duxbury. I hope this helps.