The U2X is a pure digital transport optimized for USB and network isolation rather than SPDIF/AES. It uses dual femto clocks, one for PCM, one for DSD and provides 10 MHz external clock input/output, which allows sync with a master clock for even higher precision.
So its horses for courses. I can only relate how my search went. The comparison I made with the X1 and the A20 was not so much about which was better but which difference fitted with my ears and which offered the best synergy within my system. I preferred the A20 to the A30 and then realised why I was leaning to the X1 it was the fact that the A20 was a little smoother than the A30 but the Lumin offered an even more fluid organic presentation which for me at least was less clinical than the A20 and even more a contrast to the A30.
Don’t misunderstand me, had I opted for any of these three products I would have been very happy indeed but being given time to understand their nuances and contrasts over time with my eclectic tastes was instructive. Ultimately, it was the Lumin X1which made it both the easy and difficult choice.
I am not sure how this will go for you but I would think we are comparing Apex products and it will come down to personal engagemnt more than technical prowess.
I cannot comment on the service aspect from these companies other than to say, I havent needed to speak to Lumin because the unit has been utterly faultless and recieves regular updates. Early in ownership I reached out to the company about whether I should keep the unit switched on and recieved a detailed response less than an hour after my email went to them. That’s about it.
So good luck with your choice, I rather doubt you will be disappointed with either of these great products.