@duffer5 Yes me too.Very much so,hehe.
Back to the FMC boxes.
I have some good news.
The coolest thing is that with the FMC boxes Audirvana 3.5 works without problems and runs totally stable as Roon.
I'm surprised myself and of course it's good as an inveterate user.

The good thing is also that I can set exactly what I want in Audirvana 3.5 in the upsampling.
Here is a picture of it:
And the quality increase in sound has also grown again well with the Fmc boxes.And much better and Audirvana 3.5 typical.
The bass is much fuller, more powerful,more rich.
Mids/vocals on point with lots of flow, rhythm, great macrodynamics and good timing,rich timbre and good seperation of instruments.
Treble is sweetened with great low end, also accurate and on point.
Details are very well represented, the beat and timing are also very good.
The rest is smooth and mostly buttery in execution maybe a tick bright,less warm,but still good.
Roon:
As for the upsampling I still do not know where to set it exactly fix.
Relatively under device setup right below is all I could find so far.
Nevertheless Roon does what it wants.
It does not sample me on 32/96 as I want it but plays sometimes Mqa, then again Pcm 44.1 khz and so on.You can also hear it directly out.
It sounds generally not bad but is andersst.vorallem because of the constant switch in sampling, that bothers me.
Why? Because somehow you can't really lean back.
I miss the fundamental tone to lean back.Roon obviously can not.
The bass is a little less full in direct comparison to Audirvana 3.5.
The mids/vocals seem a bit more meek.(With Mqa, vocals can get under your skin very well than without Mqa) Audirvana brings much more character in for it somehow.
In some points i find Mids/vocals a bit harder on roon.Sometimes the Voice sounds to clinical and not smooth and rich. (Not so my personally taste)
The treble is also very good and a little less sweet and also harder I think.
Details are very well represented, the beat and timing are also very good here actually everything is right.
The rest is soft and less buttery soft rather harder, and again a delicate piece brighter than Audirvana which is also at the expense of heat, so more neutral, but still good.
The whole thing is amplified again when the R26 in the setting, Attenuation is OFF.
Here is the setup as I tested it today:
The Attenuation function is and can be dangerous for headphones/speakers if you had it ON and opened the potentiometer on the amplifier.
UNCONDITIONALLY turn it back when you turn it OFF again.
I almost wrecked my Zmf Auteur because of this.
ATTENUATION causes when it is on the main gain takes back at the R26.
For this the poti must/can be turned up more.
I find when it is ON the details shine through a bit better and generally sounds a bit less harsh and softer and sounds more rich.
At the Feliks Euforia I am with a 300 ohm headphones in normal operation at 13 o'clock position.
This bothers me a bit it could have been a tick better adjusted but is now so.
On the other hand, it also causes that the headphones / speaker does not necessarily drive to full (hot) as long as you do not set anything in active mode to OFF.
The FMC bring the R26 totally in drive and I like what I hear under Audirvana 3.5.
Would not have thought that there for 100 $ / € again a good increase comes together.
Although the optical cable is quite cheap it does a very great job on Audirvana 3.5.For Roon I find it too hard for my taste.
I think with the Finisar it is again a zacken tastier like a well matured wine or whiskey.
Regarding the operation of the Fmc boxes on the powerbank.
I have a box connected to it on the "good side" and the power consumption is really minimal.it has been running for 4 h and still have full charge.
Am I personally satisfied? Yes totally,not only because I can continue to use my Audirvana 3.5.Also the sonic advantage has grown well.
Thanks goes to
@duffer5 @Dandoudou and also all others where helped me to understand the technical and otherwise have contributed, thanks guys.