Spotify Connect is now available on the 8C's with firmware 2.2, along with many improvements!!
Great news, Massimo! I have a pair of brand-new D&D 8C sitting unpacked in my apartment, so I am very excited to get them upgraded and going!
I think you'll find upstream chains vary greatly with what people listen to. Personally I use them with my own home made DAC/Pre, but that's only because I also use a turntable sometimes. If I were just listening to streaming / TV I'd probably aim for something all digital. Currently the biggest downside to the 8Cs is a lack of an external easily to use volume control ala Grimm Audio and their LS1 remote. So unless you plan to stream only via Spotify / Roon you will need an external volume control.What is your upstream chain?
I plan to get a decent R2R DAC and wondered if I'd need a preamp for them and which one to get.
I can't find information about D&D 8C analog input impedance in their manual.
Firmware 2.3 has been released: https://support.dutchdutch.com/release-notes-d-d-8-series-firmware-2-3/
The biggest changes are bug fixes in REW interfacing and an option to set a fixed volume level for the physical input (AES3 or analog), in order to use it with an external volume-controlled device.