Disclaimer! Sorry for being a ‘non-audiophile-gear-proponent‘ in this matter.
But why would you need a DAC, when you are planning ro use the 50’s/90’?
They already have a ‘DAC’ built-in.....means no matter how you feed it, the ‘sound’ will be processed there.
All you need is something that lets you transport the sound (= the digital stream) into the speakers.
Using the digital/optical output of a Chromecast Audio device could do that - it could even function as a Roon endpoint, if you are into the possibilities of Roon and its gui.
This Darko video gives a bit of background for Chromecast and Roon Ready:
link
If you want to take that a step further (which I would do), get a Beosound Core and use the digital/optical output there to connect to the 50’s/90’s.
The built-in Chromecast support can serve as an endpoint for Roon....in addition to the Airplay, Spotify Connect and TuneIn options there.
If you want a handy volume control, just use an Essence Remote or - even better - the new Halo remote.
No need to go grazy on ‘audiophile gear’, when B&O offers all you need.
You could even connect a turntable to the Core....if you are into that, too.
Darko was mentioned earlier. He recently made a video about the Naim’s Uniti Atom. You can read it here (do watch the video too).
link
However you won’t need the DAC, the amplifier and the display built-in there and you don’t need to pay that much.
Why go over the water after water, when B&O already offers, what you’d need.
For desert......those of you, who have a Chromecast dongle connected to their BV or built-in AND are interested in Roon, please watch this video;
link
MM