If DoP works fine for you and you don’t need to play more than DSD128, then use DoP. No reason to use the old dCS standard. I don’t think you could have got DSD256 from Linux via dCS protocol on DA1.
You can use native DSD if you direct connect the DA2 to Roon on Windows, or if you use our Lumin U1 / U1 MINI streamer, since we have recently added specific native DSD support for McIntosh DA2.
A likely reason between the different USB behavior of DA1 and DA2 is that they use different USB processor chips.