In case anyone is interested, I recently tried this exact setup (Computer USB output routed through a USB-Toslink converter (Douk Audio U2) then connected to Loxjie A30 via Optical input) and found the sound to be noticeably improved in comparison to connecting to the Loxjie directly via it's USB input.
For context, I bought the Loxjie A30 about a month ago intending use it for 2 purposes: 1) As part of a desktop system connected directly to my Mac via USB, and 2) As part of multi-room system connected directly to a standalone music streamer via digital input (coaxial).
I immediately noticed that audio files played through my Mac via USB had a slightly lower volume output than identical files played through the streamer, which I assumed had something to do with the output levels of each device. But even when I adjusted the volume to compensate, I noticed that the sound played through the USB connection was noticeably less clear and dynamic than the digital connection, and couldn't figure out why.
More out of curiosity than anything, I decided to see if I could find some way to convert the USB signal to optical or coaxial in order to connect to a different input on the Loxjie. I honestly wasn't expecting much difference if any, but after converting the input signal, the difference was immediately apparent - much fuller and clearer. Like not subtle.
In addition, I noticed that when connected via the USB input, the display merely says "connected" but when routed through the optical converter it displays the actual output signal (44.1KHz, etc.)
I can only conclude that the device is set up in such a way that the signal received via USB input is processed differently than the other inputs. Why they would do it that way I have no idea, but I don't know how else to explain it.
Overall, I still think it's a great sounding little unit and don't regret buying it, but just be aware that if you are considering this device and planning to use the USB connection as your primary input, you may be disappointed unless you're willing to shell out some extra $$ for a USB/Toslink converter.