A standalone DAC makes a huge difference in SQ over using a component's onboard DAC. I replaced a combo Headphone Amp / DAC with a Denafrips Pontus II and it was day and night. I run both my Buesound Node 2i and Audiolab CD transport into the Pontus and have never looked back on my decision. Which DAC to buy will depend on your listening tastes. Denafrips makes R2R ladder DACs which are described as having a "natural" sound. If you're on a budget, the Ares II is their entry level DAC.
