Yes ADM is active, not Disabled, in preferences.  What I mean is that ADM from Nuendo is not controlling TotalMix.  Normally when I arm a Nuendo track, the hardware Input Fader on TotalMix for the associated Nuendo Hardware output on TotalMix responds  to match Nuendo's fader/pan - and it does this properly with and the FF UFX+ on USB3, but when using the Thunderbolt connection - nothing happens; ADM does not work.  I am using a Thunderbolt 3 cable (USB C style connector since the PC is new) and an Apple Thunderbolt 3 to Thunderbolt 2 adapter connected to the PC.  Could that be an issue?  Every other feature of the UFX+ seems to work fine using this TB connection, just not ADM.

Thank you for the help.

Thank you for the reply

No ADM does not work at all - faders don't move and there's no audio sent to the Cue outputs.  If I use the exact same settings with the USB connections, it works fine.

I am sending a test tone into an input and I see the it on the TotalMix meter and on the armed track meter in Nuendo.  I enable the cue send in Nuendo and normally that would send audio to the TotalMix output that is assigned to that Cue, but it doesn't.  There's no sound and no level on the TotalMix meter.  I have been doing this for years with a FF800 - not sure what could be wrong: driver problem, cable problem, TB2 to TB3 adapter problem - it's an Apple adapter and I don't see any other way to connect a TB2 output to the newer style TB3 inputs.  I'm also noticed some clicks and pops when recording and playing back the test tones.  Will take a bit of digging in to find if is the recording or playback - waveform pictures in Nuendo look OK.  Will have to check the project on a different setup to know for sure.

If this feature definitely works then I think it is a cable problem and would appreciate suggestions for reliable cabling.  Thanks.

Update: so the recorded audio using the TB connection plays back fine using the USB connection which means the TB playback was the problem.  So that's ADM and audio playback from Nuendo that are having trouble. I'm going to try the Apple official TB2 cable on Friday even though it will ultimately be too short - I need at least 8 feet and better 10 feet to get the computer out of the control room.  It's not that noisy but I don't like stray noises when mixing. 

I also just got a 10' USB cable and it is even worse: it breaks ADM as well as causes continuous static making the UFX+ unusable. The difficulty of finding suitable cables is starting to really worry me.

Also good news on USB3: got a 6' extension from "Cable Matters" (they got that right!) that seems to be working well even though I'd rather not do that, but also got a USB3 C to B cable that is doing well also.  I'll test the Startech TB adapter when it comes but given the high price of TB adapters and TB2 cables, I may just send all that stuff back and stick with USB3 on PC and leave the Apple TB ports to Apple and Macs!

I just did a test of 96 tracks of OSC tones from my converters @ 128 sample latency for 3 minutes - super boring to listen to but easy to hear glitches - recording and playback flawless with low CPU Load on the Nuendo Meter, around 20% maybe.  So this is looking very good now.

While we can't fix TB for you, we can fix ADM. Due to a simple typo in TM FX it did not work with Thunderbolt. A driver update with a newer TotalMix FX will fix this soon.