If you have an external then the sound is hitting another source again so it may well hinder the SQ. The less loops that sound has to go through, the better the quality. Obvious I know but this is when quality of leads comes into play. My HDMI lead from my cable box to HDTV cost me £95 at the time (18 months ago) that would have been about $140 dollars for a 1m lead.
If you are using good quality gear then your interconnects should be as good as you can buy too.
“A cynic by experience, a romantic by inclination and now a hero by necessity.”