Die DM8000 hat keinen HDMI-Anschluss und kann definitv kein HDMI-CEC.
Es gab (gibt?) da mal Ansätze für ne Bastellösung per USB mit entsprechendem Adapter und Ansteuerung per Plugin, aber mit den alleinigen Hardwarevoraussetzungen der DM8000 geht es nicht.

edit:
gefunden: Hdmi-Cec

Sorry for re-opening an OLD thread ... and sorry for English reply - but I have an answer.
I found this while looking for a guide to do the same thing.

Set up :
Standard DM8000 (which only has a DVI port not a HDMI) running OpenPli 7.3
Sony Bravia TV (2019 model that does CEC HDMI)
Pulse-eight CEC HDMI usb plug

On the command line install the CEC utils:

opkg install libcec

The kernel driver that turns the HDMI CEC codes (via a fake serial port) into something you can read is not loaded.
you can see this by doing

ls -l / dev / ttyACM *
You will see no devices

We need to load a module from the kernel. So look in:
ls -l /lib/modules/3.2-dm8000/kernel/drivers/usb/class/
And we see
cdc-acm.ko

you can load this by doing
modprobe cdc-acm

now you should see a dev / ttyACM0 (or similar)

running:
cec-client
will now find the device and show you the commands from the remote (example press the yellow key):
DEBUG: [ 41565] key pressed: F4 (yellow) (74) current(ff) duration(0)

Now a fairly easy script will find these lines and turn them into command in the DM8000.
I couldn't find a direct way of entering commands so I used the webif system.
It is already setup that if you are coming from 127.0.0.1 it will allow commands without logging in.
I ran the web pages through NetTools and caught the remote control codes and turned them into a script.

So as an example - you press 'yellow' and this happens :
"F4(yellow)")
wget -O /dev/null 'http://127.0.0.1/api/remotecontrol?type=long&command=400'
;;

*** It works ***
if anyone wants the script, let me know and I'll publish it

Here is the script :
github.com/Ed-o/cec-dm8000