I have the ST (basically the same thing) and in the past people who have purchased an O2 or an Asgard have been very disappointed in their purchase. To them there was no difference between the STX and the Schiit Asgard or the O2, and they felt like they had just wasted money. If you'd like you can change the sound of the amp with a few OPAMPs. You can read about it in the thread below.
Yes, but the ugly truth about computer sound cards is their horrible isolation from noise. I spent endless hours to get my DG by Asus to get somewhat silenced, but failed. A purchase of the DSX didn't prove any better, nor the U3 by Asus. In the end, I just kept the DG in place and use it to power the speakers built into my monitor. While the Schiit Magni and Modi are being used to provide audio bliss. But, best of all, I don't have anymore headaches trying to sort out the noise issues, memory conflicts as well as ensuring I have the latest drivers to keep the computer audio up and running. Moving everything out to the Schiit and just keeping the USB "umbilical" cord connected to my computer has made me a very happy man.