using the razer tiamat 7.1 with the sound blaster z card. cant get audio to play through all channels at once. ive got the msi 970 mobo and am running windows 10. theres enough plug on the card for all the headphone jacks and if i unplug the speaker out jack then the mid/low range sounds play, but as soon as i plug it back in it switches to the high range.
You need to use a software mixer to convert stereo to 5.1/7.1. I have the same headset with an ASUS Phoebus soundcard, in the ASUS software it can convert stereo to 7.1, same as if you had a 7.1 speaker setup. You can't think of the Tiamat's as a stereo headset, they don't work like that. Also don't expect too much as the sound quality for music is not that good.