Do you really mean that you are going to encode to Dolby specifically, or are you just looking to do 5.1 / 7.1 surround in general? Those are two different things.
Nuendo has built-in surround panners and you can use those when mixing. All you have to do is set up the correct main output channel size and route your signals accordingly. All you need on the hardware side is enough outputs.
If you need bass management and control over delaying channels/speakers etc that can be done in the Control Room section with the bass management plugin.
Perhaps I’m not fully understanding your question…