I recently build a studio with a MTRX with the internal 64 channel Dante card and a Focusrite Red4, that handles the DA/AD via Dante, instead of having the AD/DA options for the MTRX, which cost way more. Not the same league of conversion, but for our purpose is more than adequate. The Red 16 is also a good option if you need more than 8 DA/AD.
We also have an HDX card connected on the MTRX. The advantage of having a MTRX is that it comes with 16 AES I/O builtin, so it was a breeze to interface the Genelec´s 7.1.4 setup via AES. Another advantage is that DADman monitoring controller software comes included. It´s a great matrix for whatever you want to do in terms of routing and monitoring using all the options you have installed on the unit, Dante included and can also be controllable from the AVID Control app that you can install on a Dock or S1 tablet. Using it on the Dock, you can use the hardware lateral rotary buttons to control certain functions and also the volume knob can control the volume that goes to your Genelec´s. I find it more adequate and quick than using the soft fader on the GLM software, even if on a touch surface. The disadvantage here is that the GLM SPL calibration is overrided in this scenario.
Having one of the Focusrite Red range units also has the benefit of being able to use it in either Protools mode(Digilink) or Thunderbolt mode. Switching is very fast. So if you keep using your Nuendo/Cubase or indeed any other Core Audio software along with Protools, this is a great way of handling signals from all DAW´s. You can even run diferent DAW´s at the same time if your CPU handles it. For instance you can have Cubase and Protools running at same time.
I would stay away of using the HDX card for interfacing Nuendo/Cubase and go the Thunderbolt route instead. The HDX card is important to have if low latency for tracking is important for you and also for using AAX DSP plugins. If not and native latency via Dante is good for you as is,you can either buy the Thunderbolt Native box from AVID and connect via Digilink to either a MTRX or a Focusrite Red interface.
Happy New Year
