The D-100 specs say it offers a "maximum recording time" of 25 hours on four AA batteries, when recording in the MP3 mode, etc. etc. without monitoring - meaning, without using headphones to monitor as you record.
So, as a player, if you're using its very weak (25mW per channel) headphone amplifier, you will get something less than 25 hours of play time on four AA batteries.
Using the Line Out, I would think you might get something around 25 hours of play time - same as when recording but not monitoring with headphones - but I'm just guessing.
I know from prior correspondence with Sony support, that the PCM-M10 has s proprietary sigma-delta DAC of their own design, integrated into the recorder's motherboard - it's not a standalone chip made by someone else. I suspect this is true for their more expensive recorders, as well, including the D-100, but I don't really know.
One thing's for sure - they go out of their way to deliver a very flat, neutral, analog signal to the Line Out of their field recorders, so you can count on it being neither warm nor cold. It will probably just be more transparent than the DAC in the PCM-M10, with even a lower noise floor. Again, just guessing.