My bet is you are wasting coin getting a second DAC, but all you can do is try it. If you believe you can hear what no one else has.
This conversation has got a little interesting. On the Roon community forum, I sent a message to Peter Lie, the Firmware Lead @ Lumin Network Players. I asked him which one he would recommend I buy, T2 or U1, to go with Boulder 866, and this is what he had to say:
"Definitely the T2. There are various things that concern me with the Boulder integrated DAC, such as forced PCM upsampling in the built-in Pi. According to some reviews, DSD is also converted to PCM before playback. I don’t like these. Another minor thing is that it does not play DSD256 (although you can use Roon to downsample the DSD256 first)."
I have asked questions on these lines to Boulder about their DAC but have no response yet.