In case anybody is interested: I've come up with a solution how to mount surround speakers to the Obutto, at least at the front. I use speaker holders from Amazon Basics for the rear speakers. Costs were about 5 EU for the front 3 speakers and about 25 EU for the Amazon speaker mounts.

Front speaker holders are simply made from some aluminium strips, cut to length and drilled holes. On the side speakers, you can mount the strip onto the main screw of the screen mount, on the center speaker I had to resort to double sided sticky tape.

Pictures:

The cut aluminium strips (measurements on request, to be used in conjunction with Asus VE276Q or VE278Q screens and Logitech Z906 speakers)


Result viewed from the front


Side speaker mounts attached to the screw of the monitor mounts


Center speaker mount taped to the center monitor mount