Hello, again,

Out of desperation I wanted to be able to debug the stuff now. My first trial was to build ffado from source. I had to remove the original ffado installed by package and built and installed using the actual download (2.4.4).
The result was, that immediately things were staring to work, although I didn’t use the debug version. That would have been the second step, but -up to now- was not necessary. I was able to start jack with ffado and a buffer size of 32 at 3 buffers. I started ardour and were able to use it as usual. It seems, that the ffado build in the MXE packages is not compatible with my Ryzen while the self-built ffado is.
After a while the audio became crackly and I looked up the messages. No surprise, there were plenty of xruns. To my astonishment, after another period of time, the crackling became less and vanished. Then again crackling, followed by times with brilliant audio. This to me sounds like time bases slowly drifting against each other. I will hunt down this problem as a next step.
But hooray, the general setup is working with my new killer machine. Plenty of power, two test channels in stereo with a plethora of plugins in each channel, some VCA and foldback strips to experiment with. The result: 8% DSP usage. That’s what I wanted to see.

There is no all-in one, general, click'n run procedure for linux systems.
Without any additional information, no one could help you.
If you provide more information(which linux distro, which architecture), maybe I could help out. It shouldnt be very hard...

Thus, i do not own a FF800 or use Firewire, i was just able to compile and install the 2.4.8 version on a vm.

I took 10 Minutes to try it out for you.

BTW - The simplest way would be by using a package manger, like apt f. ex on debian based distros.

sudo apt search ffado

should give you all the tools...

I tried via

sudo apt install ffado* libffado2

This installs v 2.4.7. and all relevant tools. And as i see, there should not be any relevant changes to 2.4.8:

Changes since FFADO 2.4.7:

Make various mixer modules work under Python 3.10 and later: Presonus Firebox, Presonus FP10, Presonus Inspire1394 and Yamaha Go.

Deal with the removal of SafeConfigParser in Python 3.12.

Anyhow, i also downloaded 2.4.8, removed (as suggested in the redme all 2.4.7 stuff before) and installed the dependancies first, as described in readme:

Packages for building on Debian/Ubuntu distributions are installed with:

$ sudo apt-get install build-essential subversion scons libxml++2.6-dev \
               libiec61883-dev libdbus-1-dev libdbus-c++-bin \
               libdbus-c++-dev libconfig++-dev pyqt5-dev-tools \
               python3-dbus.mainloop.pyqt5 pyqt5-sip

pyqt5-sip was not found, but should not be necessary.

then, i ran scons in the extracted 2.4.8 dir and it gave me an error:

support/tools/ffado-diag --static > support/tools/ffado-diag/static_info.txt
sh: 1: support/tools/ffado-diag: Permission denied
scons: *** [support/tools/ffado-diag/static_info.txt] Error 126
scons: building terminated because of errors.

Although, i checked rwx permissions, seemed not to compile. But i tried to do it directly via:

scons support/tools/ffado-diag

....
scons: done reading SConscript files.
scons: Building targets ...
building 'support/tools/ffado-diag' from 'support/tools/ffado-diag.in'
scons: done building targets.

et voila... have fun ;-)

Edit: And keep in Mind from readme(!!!):

NOTE: In order to build jackd with ffado support, you have 
to install libffado before you build jackd. The backend to use in jackd is
"firewire".

You would have better asked "how can i install scons and pyqt5" instead of "Please teach me how you install FFADO. In details.".
"now i forced to come back to Win10 (i can't lose time on guessing) ...  when.. i will try to beat this problem again."
-> Kidding???

Can't loose time on people, asking questions about systems they have not setup, and can't loose time for solving their own problems.