Unable to use AMT Serial-on-LAN

Hello,

I'm facing a problem with a All-in-One desktop machine (HP EliteOne 800 G2) with no serial port available.

I need to debug some at kernel/driver level, so I need something as simple as a serial port.

IMPORTANT: I must insist on the fact that I have no choice but to use that machine.

So my options are :

1. add a extension card with a M.2 or WLAN card adapter : I tried to there's some problems with the length of my adapter...
2. use EHCI debug port (USB 2.0) : but there is no EHCI controler in that machine
3. use XHCI DbC Capability (USB 3.0) : doesn't seems to work (but this will be the subject for another post)
4. use AMT Serial-on-LAN feature of vPro to redirect serial : and this will be the subject of that post

So I configured AMT and I'm able to connect to the machine on TCP port 16992 (HTTP).

And after that I enabled Serial-on-LAN (SOL), both in AMT and in the UEFI to choose either ANSI or VT100.

Intel documentation says that when SOL is active TCP port 16994 should be opened and waiting for a connection from a program like amtterm (under Linux), but this is not the case.

It seems that AMT is half there or I missed something (like the right combination of settings).