Lumin X1 or U1 + PS Audio DSD DAC

Yes, the X1 is a very well designed product.  You get a lot of benefits from having everything so well integrated in one chassis.

Can you use an external hard drive with the X1?

ozzy

Yes, or you could do some research on the product itself.  They have a great website with lots of info.

Do you use Roon to manage your music--ie., core is running in the InnuOs?
If you use Roon and jettison your existing chain you will now need a dedicated Roon server. 
After many different configurations on Roon core integration (two different Lenovo i7 laptops, i5 and i7 full sized pc's, and finally a mac mini), I have found the best result from running Roon core on the InnuOs Zenith MK III. I would NOT sell the InnuOs if I were you.
If you got rid of all your current stuff in favor of one streamer you might satisfy your desire to simplify but you will likely take a step backward in performance.
Perhaps keep the InnuOs Zenith MKIII and your current stuff and maybe get a new rack or way to organize the layout?
Of course if you don't use Roon then the Lumin sure seems like a convenient way to go.

Yes, roon user here. I've tried running the Innuos as a core, an end-point, and as a core in experimental mode. The last option has definitely the SQ but is too flaky with frequent skipping.

TBH, there's not really any SQ diff running the first two configurations.