Fresh image with all the updates and the instructions from here https://github.com/Audio-Injector/stereo-and-zero helped (both, drivers and alsactl commands).
Audioinjector works nicely now. Will submit to successful cases, when the project will be complete.
Was ist necessary to install the .deb?
Did you test it without installing it?
If the new fresh and updated image didn’t work we have to integrate the script.
My Audioinjector Zero works without the script.
I have got an upgrade (New rpi3 B+ 2017 and Samsung EVO 32Gb MicroSD) to check the installation once again. It didn’t work out of the box for me after selecting Audioinjector (mine is stereo model) in webconfig.
Alsactl commands didn’t make any difference till I installed deb package with the scripts. Then commands work and everything starts working too. Didn’t have time to check the input yet. Will do 
It could be a B+ issue. My installation is 3B
I’ve started zynthian with Rpi3B 2015, and same simptoms, so it is probably not just B+.
Anyway, I really hope my case will help the others with same configuration to get everything to work in no time. @mheidt, thank you very much for your support and input !
Right now I am in testing state and already have discovered some things to ask in forum.
Hello,
I recently bought a Zynthian Bundle All Alu-case Kit v2, I have assembled it in a few hours and it worked at the first trial.
Thrilled by this immediate success, and having a working ‘reference’ unit, I decided to assemble a second, minimal, headless unit using some components I had lying around from a previous, aborted, try to build a Zynthian.
First of all, without the physical interface I needed to force updates using the SSH command
/zynthian/zynthian-sys/scripts/update_zynthian.sh
(http://wiki.zynthian.org/index.php/Zynthian_Box_Updating)
At each boot I had to login to the router to see the IP address of the Zynthian, because it kept changing.
After a few iterations of the update process, I logged in again to the webconf page.
Only after having enabled the output of the sound card in alsamixer, I finally managed to hear the Audio test.
Then, trying to move in the Zynthian GUI with mouse and touch screen, I managed to play with Aeolus and Dexed.
For the time being I’ve got the following issues:
My considerations:
Any suggestion to fix my problems is more than welcomed. In the meantime I’ll enjoy the standard working unit. 
You can try to connect to zynthian.local.
Sadly, it doesn’t work, not even with the official unit … I had to connect using IP.
(I have changed the name of the second unit to Zynthian_two)
Audioinjector: try to use the alsa volume mixer in webconf. It is mute by default
Display: search the forum and the page of your display. Consider that the visual orientation and the touch matrix are 2 different settings.
I only opened the alsamixer from the ssh console, is there a way to access it via webconf?
I did not even know that the 2 outputs (3.5 jack and RCA pins) were separate. I couldn’t find the schematics but I took for granted that they were just the same hardware out either in parallel or just decoupled but not separate mixer channels.
Anyway messing with the alsamixer from console didn’t enable the RCA outputs.
As far as the touch screen is concerned, I just fiddled with the rotation parameter in the webconf, but rotating the display took along the touch screen rotation.
At some point I had the display upside down and the touch screen with x/y exchanged. 
Is there a way to configure this by editing some config file from console?
To get audioinjector working in my zynthian build, I’ve needed to run these commands:
There was a bug in the webconf.
Now when you select Audioinjector in the audio panel, the mute issue is solved.
I’ve this audioinjector stereo on a 3b+ too (working) and i want to know if it’s better to use at 48khz ou 44.1 for the best latency/cpu use ? With pianoteq (at 22050) i’ve some cpu high peaks sometime without any effects, on Steinway NY, i suspect cpu temp (not oc) to reach 60 C (hot summer), but i would to know what is the best setting for Zynthian in webconf. Actually i use that “-P 70 -t 2000 -s -d alsa -d hw:audioinjectorpi -S -r 48000 -p 256 -n 2 -X raw”. It would be cool to add tweaks on pianoteq page to use all pianoteq settings.
I don’t think that you can find a satisfactory solution with a raspi3. I would buy a raspi4.
I’ve one too but it was for recycling my old pi3, so cpu is always at maximum 
but i dunno if 44,1 or 48 k is the best for audioinjector stereo, i don’t see too much difference.
I am just saying, that you won’t be able to run Pianoteq without xruns on a raspi3 no matter which settings you are using. obxd neither. But the other engines are ok.
With respect to 44.1 & 48 k it’s probably more influenced by what you are doing downstream. It’s sensible to avoid rate concertino if you can.
Yup, but on my windows soundcard latency is higher in 44.1 than 48, not so much but… Don’t have too much Xrun just cpu is always hight. So is it possible to map
52 SELECT_UP E3
53 SELECT_DOWN F3
to a cc not a note ? With my nanoKontrol2 i would like to map a CC on an encoder, can’t do cursor up and down with note or i dunno how to. I use button for now (Solo/mute). Thank’s for help.