Next best exponential DAC quality level?

I recently did a shoot out of three DACs using my Hint6 + routing each of the other DACs to analog input on the Hint6:

(1) Hint6: ESS Sabre32 -- Integrated 

(2) SMSL M500: ES9038PRO D/A   ~$400 

(3) Khadas ToneBoard(v1): ESS ES9038Q2M - ~$99

I played the same song passages on Amazon Music and was able to cycle through each Hint6 input corresponding to each DAC.

The result?  Very small difference in terms of rendering.  Maybe a more open sound stage with better overall balance using the Hint6 DAC.  The Khadas was more bass / midrange pronounced w/ a more narrow soundstage.  However, I wouldn't suggest that any were head-and-shoulders "better" over the others.  In fact, they were all pretty decent with only small nuances (certainly not worth the price differences.   

I decided to keep the Khadas for my small headphone listening area. 

But it got me thinking - how much would one have to spend to realize an exponential difference in quality?  Is the Khadas that good, or is DAC technology differences more nuanced than I originally thought (meaning, we're paying 10x for only 5% better).