Point of diminishing return for a DAC

If you have money to burn, pay over $1,000 for a any new DAC.
Not that SQ won't get better when more $ are thrown its way
but this technology is improving like crazy. 

Once again millercarbon pollutes another thread with his constant shilling of Synergistic Research snake oil.  Please stop!

You can do much better by spending more than $2500 for a dac. $2500 buys you a mid-fi dac. The best dacs are of the FPGA type which costs more and you get upgrades that improve the SQ 1 or 2 times a year for free. Also, the better dacs have Ethernet network connections.
Also, you don’t need a dedicated music server for a number of reasons:
1: you don’t want any kind of server in your audio room
2: you don’t want to use USB to any dac, it is a flawed connection

your Mac mini is fine running Roon, just place the server in a different room and connect to your dac by Ethernet, keep it simple and provides the best SQ

I would second the suggestion with a streamer and a DAC. Mine are 1:1 at around 1.000 €. 
In terms of diminishing returns it is worth noting that many more expensive DAC are based on another technology. Many DAC’s around less than 2K are chip-based, whilst some more expensive are FPGA-based, which means upgradeable. So it is not just about SQ, but also Lifecycle cost. 

Since I have recent experience from Pi DAC through DCS Vivaldi stack, I might as well chime in. I ended up with an Ayre Codex fed by a Roon Nucleus. I have been quite underwhelmed by the Rendu products - Digital and lifeless, reminiscent of the recent McIntosh preamps.
The Codex was a massive step up in musicality, pace, as well as micro detail and soundstage over every less expensive option. Meaning full up grades cost nearly to over $10k. If I were to upgrade, I have to say the DCS Bartok is the most affordable DAC through which vocalists sound human.
As a side note, the R2R people and to a lesser extent the Chord people make me laugh. 1) are you really going to find two resisters that match?
2) a billion taps does not make your DAC sound as good as anything from DCS.