USB vs SPDIF, which sounds better?

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

I just double-checked the back of my Big 7, and there is no toggle switch to switch between USB and SPDIF.  Does this mean I can only have 1 cable physically hooked up at a time?  I may need to check with Lampizator on this.

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.

My bad.  I forgot I have a remote control for the DAC.  I usually don't use the remote because I have an integrated amp, so I always use the volume control on the integrated amp, not the one on the DAC.  Using the remote, I was able to toggle the input selection.  Problem solved. 

I am a former Big 7 owner ( previously a Big 6 and an original model 4 as well... ) currently running a Golden Gate. Loved each one for their own best virtues and kept climbing the Lampi ladder... so far, so good. Big 7 is a fantastic dac with outstanding value for the money. I ran a few different S/PDIF’s from my cd transport and USB’s from my Lampi Komputer.. 
Top 3 favorites in no particular order are Mad Scientist, Triode Wire Labs, and WyWires. 
My recommendation for excellence and best bang for the buck is Triode Wire Labs... Pete makes outstanding cables at very reasonable prices... he’ll build anything you need the way you want it... has a 30 day return trial policy and is a real pleasure to deal with. 
If you’re looking for a remarkably natural presentation, I can’t speak highly enough about his products. 
PS: which DHT’s and what rectifier are you running? Just curious...
Good luck and happy lissn’n! Lissnr