I looked at the update log for OpenMPT and in 1.28 it says that there is added support for Composer 670 files. However, i cannot find any C67 files or even images/videos/information about Composer 670.
Are you sure that you guys didn't mean Composer 667? The 9-channel AdLib-only module format? Or is Composer 670 just a tracker that I missed?
CDFM (https://www.pouet.net/prod.php?which=66736), or Composer 670, is basically the combination of Composer 667 (AdLib) and Composer 669 (PCM), offering both synthesis methods at the same time. It was only used for a couple of demos and games by the Renaissance demo group, most notably for the game Zone 66. It's not very widespread - basically the only reason why I implemented this is because I wanted to have correct playback of the Zone 66 soundtrack and other C67 files outside of Composer 670 itself.
Oh, ok.
Will Composer 667 file support be added in the near (or perhaps far) future, now that we have OPL instrument emulation?
Also, is there any way to get Composer 670? Is it abandonware now?
Generally the possibility exists but it would be a low priority as it doesn't seem like this format was really used anywhere, so I'm not sure if there would be much use for it. At least ModLand doesn't have a single 667 file.
Regarding your edit: I already provided a link. Look in my first reply.