DAC diminishing returns

You are looking at this in the wrong way if you are thinking that price makes the difference.  It is how something is designed and built.  We manufacture an R2R 101D tubes DHT DAC with a separate 30lb power supply.  Not all R2R DACs sound like ours does.  Diminishing returns depends on what sound you are looking for.  Clarity, resolution, slam, dynamics, soundstage, separation of vocals and instruments, bass definition, musical, and tone of instruments such as piano, stand up bass, violins, etc.  Until you hear this for yourself, you won't know it.

I just heard our DAC on the new second from the top model of Wilson speakers.  I knew what our DAC sounded like but it was still a new experience to hear our product in a completely different system. We are always learning what makes music sound the way it does.

Happy Listening.

For the record I stream with an Ethernet connection to a raspberry pie 3 with a digihat and a Toslink connection to my bifrost.

This HAT and toslink are a weak link. You’ll get much better quality output from Pi through RCA coax (or better with BNC if DAC has it) from a different HAT like this

https://allo.com/sparky/digione.html

Another option is HiFiBerry DIGI2 Pro

To get the most from the Pontus you need a streamer transport like a Lumin U2 and the Denafrips DDC like an Iris or Hermes running I2S to the Pontus, otherwise you are driving it or even the Bifrost in 2nd gear.

Does the significantly higher cost justify what might be a marginal increase in sound quality?

Do this test and see if you get it right 100%. If not ... no need to spend more money.

https://www.npr.org/sections/therecord/2015/06/02/411473508/how-well-can-you-hear-audio-quality

Of course if you just feel this itch to pamper yourself and get some nice new gear, that can be satisfactory all by itself.

What is your budget?  I would recomed you buy a DAC from a dealer with a return exchange policy and try for yourself.