Dungeon Master (currently) works with CT Raw images made with a real Amiga; there are tons of them around (and many different revisions), so imho just pick any of them
DTC will be updated later to produce the same result, and you might as well just... oh, let's just wait for another surprise coming - don't want to spoil it
But regardless, we need more DM images as well in stream format, so would be very useful to submit those.
Just to make sure: for imaging you use the latest DTC, right? That way preservation settings are automatic if you specify stream output - but you can explicitly disable that behaviour. Older versions of DTC had to have the preservation settings explicitly enabled... it's better the way it is now