Buying the STX and the O2 is moot, as the STX already has a powerful amp, and the O2 isn't exactly a good match for the K702 FWIH. If anything, you don't need the STX. Since you're using an external amp, buy something like the DG instead. Also, it'd be best if you bought an external dac with an optical input, that way you don't have to double amp from the soundcard to your amplifier.
Something like the DG -> optical out -> dac with optical input -> amp
My motherboard does not have a PCI slot so i would need to go for something with PCIE 1x like Asus Xonar DX or Asus Xonar DGX which should be fine aswell instead of the Dg ? Which amp should i get then if not the O2 ? And I dont really know which dac i should take so can you give some examples. When you say optical out thats just a cable between the soundcard and the dac and then another cable between dac to amp and then headphones ?
Edited by Hoffen00 - 11/22/13 at 5:52am