Digital Interface

I have been doing some research on trying to improve the sound quality from my PC to my DAC. I am pushing digital audio from my hard drive through the computer and also use Spotify through the computer often. I thought about possibly putting a digital interface, such as a "Singxer SU-1", between the PC and DAC. There is mixed information out there on if this adds much value. Anyone have success here?
It is self evident that a DAC designed for high fidelity should reject jitter. After all, jitter is nothing new and if a $150 Schiit Eitr can fix things then it is self evident that the manufacturer of the DAC could improve their design such that band-aids were not necessary. If Schiit can do it so cheaply then so could the manufacturers a $2000+ DAC.

I would love to think that a $150 DAC could eliminate jitter but that is just not the case. Jitter is an ongoing battle in all sectors of digital storage and carriers I'm afraid and none more so than DACs . I happen to use my computer as a Digital Audio Workstation and have invested very heavily in jitter busting software from Mark Porzilli of the Memory Player fame. The software was definitely not cheap but the limiting factor is always going to be the USB ports wich are attrocious for jitter.I have what most people would say is almost zero jitter inside my PC so how come DACs of all price points sound so different through it. The answer is I'm afraid jitter related so when I say the PS Audio Lan Rover makes a difference I do mean it. My friend has a PS Audio Direct Stream DAC and there is a definite difference between the Lan Rover being inserted and taking it away , it is cleaner with it in circuit. I have tried it on a few DACs as I have a good friend who is a HI Fi  dealer and he let me try it out on a few of his and much to his dismay he had to agree that it did make a difference and a few of those DACs were in the 3 to 7 thousand pound range. The only DAC that the jury was out was with the Gryphon Kalliope DAC which was neither better nor worse but that is an eighteen thousand pound unit. I have even seen PS Audio advertising their DAC with a Lan Rover hooked up to it.

So so we agree! 

The Schiit Eiitr is just a USB bridge to coax - so it probably will improve the PS Audio Direct Stream too.
DACs mostly all need a band aid to actually work properly but there is no reason they can’t work properly without / the Gryphon Kalliope being a good example!
Why not use a fiber optic cable?

Yes, there are several DACs on the market that have jitter reduction and re-clocking or re-sampling. These can be good if you have a poor digital source, but in the end they are just a "fix a crappy signal" solution. They will never as good as when the signal was clocked and transmitted properly in the first place.

The Singer SU-1 and the Schiit Eiitr are great devices for taking a USB signal and re-clocking / converting it to S/PDIF (which is closer to the original digital data and clock timing). These are good devices if you are limited to a laptop.

If you have a PC, I would recommend looking at a better audiophile USB card. Such as JCAT or SOTM usb cards (PCIe).

If you want to skip USB and use S/PDIF directly, the Asus Essence STX II card has a very nice S/PDIF output (I use this and it’s excellent). Or you can go all out and get the latest Pink Faun audio bridge with an S/PDIF plug-in module.