hi Roobbe and welcome to LQ !!
i am not a guru but i think your problem is :
while you ran enlight there was a sound server in the background: esd or something like that.
now with flux you have not. in fact is not necessary to hava a sound server.
it depends wich sound system you are using: OSS // ALSA
your kernel version is also an important information.
as you probably know, sound is something tricky in linux.
try to give some more inputs and the gurus around will talk to you...