i think ur stx is fine its an all in one audio solution..
you can drive most headphones out there including the hd 650 and akg 701
you can connect stereo rca out into an integrated amp and bookshelve speakers
you can switch those setups in literally one second via computer and the dac on the stx is not paid as well ive compared it to the wolfson 4871
i dont think u really need to connect ur coppers to the pc just connect it to an pmp like ipod