Sorry for late response: marami na pala nagpost, sorry sa confusion.
My setup is: PC (asus stx soundcard) > Rega Dac > amp. I use the digtal out (spdif) of the stx soundcard to connect to the Rega Dac.
Comparing it with asus vivo pc (without the stx soundcard but with spdif out) connected to Rega Dac. And to my ears, the desktop pc with stx soundcard convincingly wins, the sound was fuller, more detailed, immediately noticeable is mas malakas tumunog stx soundcard. I compared it again to same Desktop PC (with stx soundcard) this time using a USB Dac and my verdict stays.
Again, my main DAC is Rega, its just a question of which PC has the cleaner, refined source. All I know is that the stx soundcard really complements my system. Pasensya na, hindi ko talaga alam yong mga conversion terms