After having owned two Mojos for two whole years, I can't believe I missed out on using optical. I naturally chose USB from PC, and part of that decision was my motherboard which has no optical.
However after starting to read the Hugo 2 thread, I re-read opinions about optical being better. That being due to noise on the USB power lines, and PCs being full of noise. Anyway I have singled out the Audioquest JitterBug on my to buy list. Probably order today or for sure in next three days.
I also bought an adapter for my PC which will give me an optical out. Only a cheap thing on ebay,
https://www.ebay.co.uk/itm/SPDIF-Optical-and-RCA-Out-Plate-Cable-Bracket-for-ASUS-Gigabyte-MSI-Motherboard/182484182912?ssPageName=STRK:MEBIDX:IT&_trksid=p2060353.m2749.l2648
It takes optical from a header on the motherboard, and sends to rear of PC. However I am concerned about noise inside the PC again, and the device will use power rails from the motherboard header. This may interfere with the signal before it's converted to optical, before being sent to DAC. (I did buy a very good power supply though, and hopefully that will reduce noise.)
Another option is to buy a lower end quality sound card that has shielding and optical out. Getting kind of like a dog chasing its tail though, meaning looking for solution after solution.
However the results should be getting more sound quality from the Mojo. It makes me realise that I have not heard the Mojo at its best yet. Considering how it sounds already, that's quite something to think about. .................. Still sulking a bit though.However I decided long ago, that my next PC build will have a motherboard with optical. All should be well again in the universe then.