Malfunctioning SMSL SU-9n

I recently purchased a used SMSL SU-9n on audiogon and long story short the optical/toslink input is malfunctioning but the USB works well. I tested multiple cables, sources, and I looked through the menus for simple solutions to no avail. All of my other cables and components work as intended with the SU-9n taken out of the system. However, when the optical input is selected on the SU-9n the audio cuts in and out at different intervals. Have any of you had this issue?

Here is a link to a YouTube video so you can see and hear the malfunction.

SMSL DAC malfunction


A list of the gear I used for testing. 

     Rogue Sphinx v2 amp
     Elac UB5 speakers

     Oppo 105d
     Caldigit TS3 plus - USB hub
     Macbook Pro
     LG C3 - TV


I had the same issue with the SMSL D300. Mine was a month out of warranty.
tried everything to get the thing serviced no one from Amazon / Seller on Amazon or SMSL seemed to care. So now I have a $400 USB Dac only. I’ll never buy SMSL again. 

I’ll stick with Schiit audio for DACs I don’t think Schiit would leave you hanging like SMSL did to me. 

As I've continued to research that is also what I've come to understand. I am frustrated that I was sold a faulty product especially because I specifically purchased it for the functionality of the optical/toslink input.