I anticipate you will receive additional DAC suggestions not on your list plus suggestions to change other components in your system. I have an X1 plus other DACs--unnecessary extravagance I know. I have not owned nor listened to the other DACs on your list. Your overall presentation will be system dependent. Will you be able to audition the X1 and/or DACs on your list? If so, inquire how many hours have been accumulated on demo unit(s). I found the X1 began sounding much better at 200 hours, but really settled in around 400 hours. I do not see a server listed--what equipment are you using there and which services are you using?
I currently am using Leedh processing with my X1 but have used preamps with it as well. Leedh is quite good. I believe you can use it with the D2, but you are using an integrated, and do not know if you can use it bypassed for only amp to try. If you can, I would expect a difference in presentation, which may tilt more to areas you wish to increase.
Eventually, Lumin will bring a new flagship to the line, but the X1 will still be a fine sounding piece. Lumin has a history of supporting legacy devices. The Sabre 9038Pro is quite capable with resolutions higher than my streaming sources and higher than any of my music on my server hard drive.
Wish you the best in your journey. Please keep us posted on what you land on.