I have compared my SOnore Optical Rendu and the Lumin X1 using fibre directly from my network switch. Both sound different and are equally good.
However, I also have a PlayBack Designs Streamer-IF that I bought for $2k. I am only using it with SPDIF out and Ethernet into the streamer (no fibre). I do not know what Andreas K. has done inside that unit but that streamer sounds amazing. Sort of in-between the sound of the smooth and refined Sonore with the loud and brash X1. I plan on eventually getting the PlayBack Designs Dream DAC and then use the fibre stream out of the Streamer-IF. That should be even better.
My Streamer-IF is the previous streamer model PBD sells. I think the new streamers they sell can be used with many more output types, including USB. I would look at them even though they are seriously expensive.
Playback Designs | the finest audio playback in the world
I would think this streamer would work well even connected directly to a noisy computer given the reputation of the designer.
BTW - the Lumin U1X seems to me the internals of the Lumin X1 streamer (what I owned)