The choice of surround system is completely independent of the projector.

The basic rule for sound systems is that the "complete systems" (e.g. from Samsung) that are available for approx. 500. CHF are all no good.

And since, in contrast to the projector, the loudspeaker boxes last an extremely long time and are almost never technically "overhauled", you can keep them for 20 years or more without any problem. It is therefore worth investing a little more in the sound system and buying a decent amplifier (e.g. Denon AVR-X1400H; approx. 550.- CHF) plus 5 decent speakers (e.g. Canton; together approx. 1200.- CHF) and possibly a suitable subwoofer (approx. 500-800.- CHF).