[Charlie Sheen]

Hey guys. I just got a Beyerdynamic DT 990 Pro 250 Ohms + FiiO E09K. I already had a Xonar Essence STX, but i didn't l ike the amp very much. However, this soundcard has a pretty good DAC. Anyway, I just want to use the E09K as a Amp, and the STX as a DAC. Which connections I use, and what cable I need? Thanks!

 

[TrollDragon]

RCA to RCA Patch cord, Line Out from the STX to Line In on the E09K.

 

[Charlie Sheen]

  RCA to RCA Patch cord, Line Out from the STX to Line In on the E09K.

Can you post a picture of this cable? Thanks

 

[TrollDragon]

Something like this will work just fine!

 

[PurpleAngel]

  Hey guys. I just got a Beyerdynamic DT 990 Pro 250 Ohms + FiiO E09K. I already had a Xonar Essence STX, but I didn't like the amp very much. However, this sound card has a pretty good DAC. Anyway, I just want to use the E09K as a Amp, and the STX as a DAC. Which connections I use, and what cable I need? Thanks!

The Essence STX and E09K use the same TI 6120A2 headphone amplifier chip, so I doubt you will notice any improvement with using the E09K.
And the Essence STX can not send headphone surround sound thru it's RCA outputs, only basic stereo audio.
 
Did you disable the motherboard's on-board audio? in the BIOS.
Sometimes the on-board audio has a negative affect on the add-on sound card
 
Try the Unified Xonar Drivers.
http://maxedtech.com/asus-xonar-unified-drivers/