jhg

s905x3 has never been supported and you can safely throw it in the trash, nothing will work.

You are not going to get watchable YouTube on a cheap TV box with Armbian currently.  The state of the open source video decoders (vs the generally closed source used in Android) is still a work in process.  Right now I would say the best supported CPUs are the Rockchip ones.  On the box side balbes150 is working on the Station M1/P1 and jock is working on general Rockchip TV box support.

@jhg
I understand the fascination, it is why I'm here trying to help others foster that same fascination.  But I would caution you on your expectations.  When you talk about 'desktop computer' you are likely to be disappointed.  The current state of these boxes (once you get one working) is you can get a desktop gui running, but the performance isn't going to be something useful.  They do make great servers however.  If you want a usable desktop experience you are going to need to be spending around a $100 or so for an RK3399 box which is less fascinating and a stretch on the wallet.

Are you following the instructions in the FAQ: https://forum.armbian.com/topic/17106-installation-instructions-for-tv-boxes-with-amlogic-cpus
 

@jhg If you really want to dig into this more, you would need to hook up to the colsole interface on your box.  To do this you would need to identify the console connector location on the board, solder a connector to it and then get a usb adapter to monitor the low level u-boot output.  The first stages of uboot output to the console only, then the chain loaded uboot (uboot.ext) will display stuff at later stages to hdmi.

@jhg  FYI the s905x3 cpu should be using a meson-sm1-* dtb.   sm1 is the internal code for the x3 (glx is the s905 and g12 is the x2 family).  So I would recommend starting to test with:  meson-sm1-sei610.dtb
 

This is a tricky shit that hides behind openness, but in fact tightly controls the main part-the loader. I.e., at any time, it can block or completely control any unwanted person's actions.
 
 
It's funny, you described a whole theory about freedom, and as a result it all came down to advertising and pushing aml shit. 
For your information, aml imposes its BSP shit on everyone, which is stuffed with Trojans and bookmarks to gain full control over those who use their shit. They lie to all users about their hardware and actively cooperate with those you are trying to protect yourself from.
 
In general, everything is as usual, if you remove the beautiful words about freedom, it all came down to the fact that "someone" would spend their time and money and provide the rest with free use of aml shit.