Lumin U1 vs Lumin U1 mini + sbooster?

Yes, you have to remove the switching power supply inside the U1 mini.

Then install a DC kit from audio sensibility so you can power it with an LPS. The LPS remains external. The kit comes with all of the instructions.

It's a little nerve racking since you have to cut the red wire inside the Lumin to remove the IEC. But overall, it's pretty simple, and you get a reference streamer at a fraction of the cost of a U1.

That’s what I was thinking but it sounds like the kit is well thought through. I’m guessing that cutting that red wire will negate any warranty from Lumin so buying second hand isn’t really a compromise.

I can confirm that the U1 Mini mod is straight forward and relatively simple. I would recommend getting a used unit here on Audiogon or even my already modded unit (Lol) and not worry about warranty. 
I agree with all the tweaks being discussed here and they do enhance the performance of the U1 Mini but not to the U1 level. Also, those very same tweaks can be done on the big brother U1 to make it even better if you’re seeking the ultimate performance from a streamer. These tweaks when applied on the U1, will make it significantly better than the Mini, by a significant margin. However, if you’re just trying to get the most of the U1 Mini without spending a lot, then stick with the tweaks suggested here and be happy! $5.9k is a big chunk of change for a digital streamer. 

mrcypruz, this is why I brought up the Bricasti M5. It sells for a little over two grand and with a possible discount even less.