Best digital cable $300 or under new or used?

Creative Cable Concepts Green Hornet is one to look into.

Granite Audio - because they are as close to true 75 ohm, TDRed for quality control, as they come.

You would be amazed at how many audiophile digital coaxial cables change the sound from specs as they ain't true 75 ohm. Our Az AV Club tested a bunch of cables a few years back and I hate to say it, but often the more they cost the worse they measured.

Look for a used Stealth Varidig - the original not the new one which is well beyond the $300 mark... True 75ohm and awesome

MAC DIGITAL-H SOUND PIPE

www.myaudiocables.com

You may wish to add Audioquest Eagle Eye (75ohm) for digi-coax and AQ Raven for AES/EBU to your list. They both do a tremendous job in all the areas you are looking for.

When I added Eagle Eye for DD 5.1 and DTS from my transport
to surround pre/proc, I was very surprised at how much of a
difference it made in my HT.

Raven from my transport to my DAC was equally stunning.

You can often find these cables in shorter lengths used
on A-gon at your price point of about $300