ZebrechAune X1 looks really nice, but only had money for the FX audio DacX6. Is there really a major difference between a DAC amp combo that costs USD 60 or one that costs USD 500 or even USD 1000. With the advances in DAC technology I am sure I would fail any blind listening tests conducted with DACs only, but how much difference does the amp make with the HD6XX. Anyone with experience able to objectively quantify the improvement?