I am upgrading my Genelec monitors and will drive the new gear digitally over AES/EBU. My short list is topped by the Matrix Audio X-SPDIF 3. Any comments, observations or alternate suggestions welcome!
What are your format and sample-rate playback expectations? AES/EBU transmission is limited to 192kHz and DSD64 via DoP 1.0… Why not just feed the monitors with high-resolution analog signals from your DAC in-order to take advantage of up-sampling beyond 192kHz and higher sample-rate 1-bit DSD playback resolutions? What makes you think that the DAC in the Genelec’s is better than your DAC connected with good quality interconnects… Can you not bypass the DAC in the new monitors and feed them with analog interconnects?.. Seems feeding them a digital-signal is a step backwards…
In these monitors the balanced analog inputs are converted to digital, as the onboard DSP implements the crossovers (as well as time- and frequency-domain room correction). They don’t have a DAC in the conventional sense as the amplifiers are PWM.
And TBH, I don’t have a DAC. 
Seriously.
I am not looking for any magical audio voodoo, just a well implemented USB-to-AES interface.
Mutec MC3+USB
Thanks @Agoldnear and @jmtennapel, the MC3+ and its little brother MC1.2+ are on my short list!
6moons review
https://6moons.com/audioreview_articles/mutec/
UPDATE: Matrix Audio X-SPDIF 3 works great with Audirvana, courtesy of Thesyscon ASIO driver.