Despite Win10 not being supported, I managed to get the EUCON protocol installed and WORKING. I ran the Nuendo 6.5.40 update, which contained the EUCON 6.5 32-bit & 64-bit adapter. I installed only the 64-bit adapter. Once I restarted the machine, Nuendo had the EUCON protocol available in the device list.
I have not experienced any issues with running Nuendo 6.5 NEK (64-bit) in Win10Pro. My sessions range from 12 - 64 tracks running multiple plug-ins from Izotope, NI, EastWest, Line6, etc. In fact, my Win10Pro machine runs Nuendo smoother than my old Win7Pro machine. The most significant different between the machines, aside of the operating systems, is the processors. The Win10Pro machine is using an AMD FX 9590 (8 Core) processor and the Win7Pro machine is using an Intel Core i7 (12 Core).
A bit off topic, however, most of what I do is video post production. Both of my machines, old and new, are being used for this purpose still (depending on what location I am working in). If rendering a video with non-GPU accelerated plug-ins, the AMD processor is able to render about 9-10 times faster than the Intel chip. If rendering only GPU accelerated plug-ins, there is no significant difference.
When using EastWest products, the Intel chip could never keep up with the demands which caused a lot of lagging and studdering; especially when 20+ EastWest plug-ins were loaded. I have not experienced any issues with the AMD chip. Same can be said for Izotope plug-ins even when running multiple instances of RX Denoiser. Yes, granted, I should be processing the noise reduction offline, however, I prefer not to in case I should run into any particular portion of the audio where the denoiser should have unwanted affects.