Typical Nuendo system uses the Nuendo/RME 9652 Hammerfall card as the PCI soundcard, which has 24 tracks of ADAT lightpipe at 48K, as well as word-clock and SPDIF. That lets you use anybody's converters.
Lots of people use Apogees, and there is an Apogee/Nuendo project bundle available. But almost all the converters out there, even high-end ones like Mytek and Prism, offer lightpipe now.
I use the Steinberg Nuendo 8 I/O 96K (aka RME), which sounds excellent, a Crane Song HEDD, and one of those awesome Panasonic WZ-DA96 8-channel DACs (discontinued, impossible to find), so I have 12 ins and 18 outs.
