Kuky, I'm also running a X-Fi Xtremegamer sound card with driver version 2.18.15 on a Win7/64 system withA-10C Beta 4 and have the same problem. The music is heard thru both front and rear speakers but when I launch a mission the rear speakers stop working, I tried with both in 4.1 and 5.1 with the same results. I'm using a "Y" spliter of the front speakers to provide sound to my head set.