The audio engine is the same between Nuendo and Cubase.
About routing, I use output routing to have different mixes. For example, in all my mixes, I have and Stereo Out, just with my master buss chain, a "limited" out, with a limiter activated so, when I export, I have two stems. You can do the same with groups, but it's not that straight.
Nuendo 6.0.x / Cubase 7.5.x
Mac Pro 3,1 Octo 2.8 Mhz, 8GB RAM, OS X 10.8.4
RME HDSPe, UAD2 Quad, 6.5.2, Novation Nocturne (as MIDI device), Unitor 8 (x2), ESI Pro MIDI, Blackmagic Intensity Pro
MacBook Air 4,2 4GB RAM, OS X 10.9.2