I'm looking for a DAC for the HD800S. Do you have suggestions? Max 2000€. I have unfortunately NO IDEA what to try.
What about the Chord Hugo 2 or Copland DAC 215?
Depends on what you're looking for in a DAC. I would like to try a Luxman DA-250/DA-06 > P750u > 800S chain to see if it's more refined than my current rig. Never heard it, could be 10x better than what I have now but no I2S though so I wouldn't take it home with me.
If you want smooth and easy-going I can recommend the DirectStream from PS Audio, but I'm not sure how available they are outside the US (I say this because of the euro for price, correct me if I'm wrong) . I use the Jr. on Sunlight firmware and it sounds great through the HDV 820 > 800S chain. The DS goes for a good price these days, but might be a little difficult to find one in 230v for $2k EUR.
What about the Sennheiser HDV 820, opinions?
I like the headphone amp section a lot. I'm a little less enthusiastic about the DAC section. AES input was dropped, gain switch only on SE inputs. The DAC can be bypassed altogether...which may or may not ruin the purpose of the HDV 820. It's a safe option, would be a good baseline to try the 800S with and see what you like/don't like about the setup. Some like it a lot, some find it dull, etc. Main issue I have (and everyone else has apparently) with it is the retail price... 2399 euros could go towards one of those Luxman products, like a P750u

. Worth considering at around half of retail cost or less, I just wouldn't pay full retail when there are many, many more options now than there were in 2017.