Hello Reiner,
I also have the same router as you and have been powering it with an ifi x 12V, 2A power supply for a few years now without a single problem. Total of 17 clients on it, but a few functions are disabled: dect, media server and all my Lan ports except wan are limited to 100mbs. Sound wise, it was not a massive improvement.
Kind regards,
Bosko