I got a R9 290 on the Gigabyte GA-B75M-D3H and it has two PCIE slots with one running at 16x and the other running at 4x and I was wondering if I throw in a asus xonar STX will it force my 16x slot to run at 4x?
So long as the graphics card is installed in the #1 X16 slot it should not cause any issues if you install a soundcard in the #2 PCIe X16 slot. The device in the second slot will only run at normal speed but the #1 slot should not be affected.