@wig -Thanks for the cable list. I have never tried Grover Huffman cables of any type but I know many like them and believe they offer a good performance to price ratio. I have not gone too far down the road of digital cables but I have tried a few USB cables including Curious, Triode Wire Labs, Totaldac, and Network Acoustics Muon. Of those, the Totaldac seems more organic sounding while the NA Muon seems more incisive and detailed sounding but without any shrillness or fatiguing qualities. I am using TWL's AES/EBU cable and that seems to work/sound fine. Sonore wants me to try their USB cable but I have made more traction upgrading components rather than cables so I sort of stay middle of the road wrt digital cable choices.
@cdc - I wouldn't say "last 2 or 5% in sound quality" as I believe these DACs have a larger sonic impact than that, and much more than the difference in servers. I have had several pretty good servers and none of them made a discernable sonic difference, although I did hear a big improvement in moving to the Sonore Signature Rendu SE streamer. That discussion gets messy because when you say "server" many believe you are talking about a server/streamer combination. The thing about DACs is they do sound quite different from each other and while one may not generally be significantly "better" than another, they definitely sound significantly different from each other. Most people seem to have a type of sound they like, and will choose a DAC that matches that type of sound and avoid DACs that provide a different type of sound.
@bgross - There seems to be a small jam pile of DACs at around $4K. I had not heard of the Canor from Slovakia, which uses dual ESS Sabre chips and four tubes, but it has received several very positive reviews for how it sounds. Maybe somebody else with access should do a comparison of all the $4K DACs on the market.