Hi Klaus

There aren't a lot of midi controllers that you can program to send out Sysex values from faders and knobs.  However, there are some.

The most flexible way could be to use Bome Midi Translator. If you didn't want your msg to go via the computer, you could get their hardware Bomebox as well to translate in hardware.  Possibly the most flexible way, with hardware controller of your choice.  Then you could also assign output mutes etc.

Simon

Hey Klaus.  Incorrect assumption I'm sorry. Extract from the maunal below.  So in a sense it's the same as TMFX, except further downstream if for example your DAW goes haywire.

Encore SlideMate, Doepfer Pocket Fader, JL Cooper Fadermaster (all discontinued I think (ebay?))

Do you enjoy DIY?  You could do something custom based on a platform like Midibox or similar, and embed a nice big fader in the surface of your desk/table  ;-)

9.2 Global Output Level

Ganged setting of all 8 analog output levels simultaneously. This
function provides a global volume control, which is indispensable
when doing surround monitoring. The included remote control box
directly uses this function.

The level attenuation is calculated and performed in the digital domain. When using higher at-
tenuation settings most of the time, the hardware output level (OUTPUT) should be changed to
a lower setting to utilize the whole dynamic range of the DA-converters as much as possible.

There are 48 steps from 0 dB (no attenuation) down to -96 dB available. Each step is shown as
one LED in the left window. The more LEDs light up, the higher is the output level. At 0 dB at-
tenuation all 48 LEDs are lit. In the range of 0 db down to –20 dB the attenuation takes place in
steps of 1 dB.

Hi Klaus

Well, I believe it's pretty much the same technically whether done in TMFX or ADI8QS output trim, a simple * operation.  If you are worried about bit depth, you'd have to get the fader down pretty low to start losing audible resolution.  But see the point in the 2nd paragraph of the manual extract regarding optimising this range with the switched hardware output level (which is in the analogue domain).

Simiarly for years I have used TMFX with an advanced remote as my monitor controller.  What I did was use the attenuation on my mionitors (DIP switches yay, not pots - Thankyou Emes) to lower the input gain on the monitors in the analogue domain.  This gets them in the range where my master TMFX fader lives in the range of -12 ~ 0 depending if I am listening to mastered music or working on unmastered material.  I actually really like the advanced remotes large flat wheel pot as a monitor control - it sets next to my keyboard and it's easily operated with one finger like a fader.

What all this doesn't buy you is an analogue saftey net of a dim, level or mute if your DAW (or DAW operator) tries to divide by zero.  However I have not destroyed my monitors yet despite some spectacular Sequoia crashes.  I mostly credit this to the integrity of the RME drivers rather than technical prudence on my part.

Your ideal scenario of the fader directly connected by midi to the ADI8QS is not bad in a crash scenario assuming the ADI8QS is still responding to midi input. 

I've had a look for passive analogue monitor controllers, but they are all variations on knobs.  Haven't seen any faders.

What about DIY lite?  Get a high quality fader potentiometer, and this box (USD 120)
http://www.midisolutions.com/prodped.htm

I had a quick look at it's s/w and you should be able to program it with the ADI8QS's sysex for global (as in all outputs) output volume which happens to be:
F0 00 20 0D 41 7F 20 00 xx F7   
where xx is the data byte in 48 steps from 00 to 30 hex. 
But the only way to know for sure is to buy it & test it out.

Simon