+1 for Morrow, that's where I started my cable journey due to the gaurantee, but I bet others (Blue jean, wireworld, anticables) could also deliver.
For me, power cables and speaker cables make the most discernable difference, that and using XLRs vs RCAs. I was shocked at the impact of power cables esp for amp and pre.
Confirmation bias story - when I decided to up my speaker cable game, I posted on the Thiel user's post for advice and happily took Eric Squire's advice and went after Acoustic Zen Hologram, used market for reasons described above. First offer I made was to a guy using these cables in a Magico/Aesthetix system with Audio Note DAC, way way out of my league. He accepted my offer, but then reneged bc he couldn't handle the SQ with different cables! I found another seller and happily hooked up my new cables to my modest system and was happy with the improvement, discernable for sure but not certain I'd be able to tell a difference 100/100 times in a blind comparison test, so have always wondered how much of this is confirmation bias. But more than anything this experience added to my amazement that power cables seemed to have more of an impact. But then I remembered I went from stock power cords to $300 used Cardas, and the speaker cable change was from a lower tier Audioquest to the AZs. Don't get me wrong, I'm sticking with the AZs, but I think this illustrates the fact that you gotta try for yourself and see, and good luck filtering out the CB!
Re digital cables, not sure if I've been able to confidently tell a difference.
All that being said, the weak link in my system might be the long run of AQ Cascade xlrs from pre to amp, I need a good 15-18' and haven't come to terms with spending the same amount of $$$$ on cable as a component. Might have to start a discussion with that question.
Once you get tired of listening to cables, get some tube gear and start swapping out tubes. To me these are great ways to exercise and improve your listening skills.