Clearaudio Concept TT subpar sound quality

+1 virtually all  of the above.  You most probably want to feed your Buchard an analog signal via RCA connectors from a conventional phono preamp (imo just about any other phono preamp will be better)  and let any A-to-D conversions happen within the superior dedicated Buchard hub.

Also, the other inputs  to your  hub are probably all superior to that 3.5 mm that your Project box requires.

And if possible, take big-greg's suggestion to dial in the Clearaudio TT with a friend's analog-based components.  

"What do you think of the standard Clearaudio MM cartridge?"

Agforte,

The Concept MM  may be  in many ways an entry-level cart with limitations, but  "Lack of clarity"  and "over-saturation"  are not characteristics that describe this cart when properly set up.

You mention one parameter that you've tried to set (vtf) but nothing about checking the 7 or 8 other factors critical to a proper setup, beginning with leveling the platter that might explain why you are getting inconsistent VTF readings at different locations.  

There is quite a bit of info around the forums and online publications concerning your TT,  and in general how perform a proper basic TT setup.  The best, most expensive cartridge on the planet will sound like rubbish without it.  Suggest you stick with what you have and learn how to get the most from it before moving up.

You've set a very low bar of "as good as Spotify".  With a bit of research and practice, I have no doubt that you'll exceed it.  Good luck!