http://dmweb.free.fr/
I just came across this site today. It is dedicated to Dungeon Master and its sequels.
I actually never knew that Theron's Quest on the PC Engine was a sequel to Dungeon Master II. Did you? It gives me a reason to fire up the PC Engine emulator again now.
And I also didn't know that another game in the series was released in 1998, called Dungeon Master Nexus. This was only released in Japan, for the Sega Saturn, and uses a full 3D game engine. I would love to see this game running, and the site does contain a link to a download of the game ISO, plus extensive details on how to get the game to run using the Saturn emulator Girigiri, although there are now better Saturn emulators available. I will have to give this a try!