USB vs SPDIF, which sounds better?

OCD HiFi Guy (Mike Powell’s YouTube channel user name) tested USB vs SPDIF cables for their respective SQ. The SPDIF cable was the clear winner, despite having the digital signal go thru a USB-SPDIF converter. The link is below:

https://youtu.be/WT465YxYr-Q

A true SPDIF digital cable is one terminated with BNC connectors. Those in the know (audioengr) would recommend a SPDIF cable having a 4 ft length. RCA connectors aren’t true 75 Ohm connectors. So if your transport and/or DAC only have RCA connectors, then just get a BNC-terminated SPDIF cable and 2 BNC (female) to RCA (male) adaptors.

(From what I can gather via internet searches, your server has a BNC-SPDIF jack. The Big 7 DAC appears to come standard with an RCA-SPDIF jack, though one can outfit it with a BNC-SPDIF jack as an optional, extra input. So you only might need one BNC-RCA adaptor in a “worse” case scenario.) 

I used a number of SPDIF cables. One is a $500 BNC-terminated solid silver cable made by Mark Coles from Sablon Audio for Here’s his link:
http://sablonaudio.com/index.php/signal

Oyaide makes a decent, $150 BNC-terminated SPDIF cable composed of 5N’s silver braid (DB-510, 1.3m).Here’s an eBay link:
https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F283160127875

Mike Powell (OCD HiFi Guy) will respond to you quickly regarding what he used for SPDIF cabke(s) if you reply to his YouTube video clip or message him here.

@respected_ent  Mike Powell goes by the user name @mikepowellaudio here on Audiogon. 

The ground loop issues of a USB cable can be mitigated by using an unpowered version (data only) of the USB cable. Several high end companies offer this sort of cable (Sablon Audio, for example). 

@respected_ent Your DAC should be used to select the digital input. 

It’s odd that such a high-end DAC wouldn’t enable user-selected options between digital inputs. I’m sure the company can assist you with this.