It all depends on what the output stream actually is.
If it is Dolby Digital, it will need to go through a decoder before hitting Nuendo.
If it is DPL (matrixed - very common on games) then you again need to decode it, or else record the stereo matrix & decode later with the Minnetonka DPLII plugin, for example.
If it is DTS, again it will need to be decoded first.
The best way is to use a proper decoder, and record the analogue output from that into your workstation.
You can try it with various hack decoders (if it ain’t licensed by Dolby Labs, it is a hack or reverse engineered) but results can vary. Most AV amplifiers can do this stuff on their internal decoders, and you can get line level outputs with no problems at all.
As the output is most likely already in a lossy format, it makes sense to use the best decoders you can and that means genuine/licensed Dolby Labs or DTS…which is what will be in those AV amplifiers.