post audio limitations of 7.5 compared to nuendo?

I wanted to make my own personal 5.1 audio DVD.
What are the limitations between nuendo and that of 7.5?

Do I need an additional plugin to mixdown 5.1 audio within cubase 7.5?
Or will 7.5 play back 5.1?

Depends on what format you want to mixdown to. Cubase can mixdown and playback discrete 5.1.

so should I just setup my new rig with 5.1 outs then select some kind of mixdown format or use an external encoder?
Sorry Im from the nuendo world and avid media composer so its all slightly different.

Thanks for helping a Nuendo refugee.

AFAIK, DVD audio accepts LPCM, or MLP, so I´d say, you could simply use the discrete 5.1 Mixdown.