Can the volume control of the T2 be set to fixed if feeding an external pre amp? Or does one just turn volume all the way up?
Yes, the volume can be fixed and becomes the maximum value of 100. No digital volume is applied at volume 100. For digital output it is bit perfect.
I assume the display shows if an MQA file is being decoded just like dsd, etc. Correct?
Yes. The display will show you in which format the file is being played.
To elaborate this a little bit: the Lumin front panel shows the MQA authentication status as well as the MQA sample rate. This works for streamed Tidal MQA, MQA downloads, and MQA CD rips.
I assume the same with D2 correct?
Yes, true for all Lumin players / streamers.