DMS is very similar, but a little different to ADF. DMS was invented back on the Amiga as a way to package disks into smaller files so more than one disk could be sent on a single floppy disk. Often you could find PD software or Amiga demos stored as DMS files and you would need to first make them back into real Amiga disks ready to use. With ADF, it was invented because of emulators not being able to read real Amiga disks.
The biggest difference is compression. DMS tries to compress (mash) the disk image down as small as it can, whereas ADF doesn't natively compress a disk image. Instead storing it bit for bit as a track by track image. The compression of ADFs comes after when you then zip them up.
And a Zipped ADF will normally be smaller than a DMS of the same disk, but both file types will work just as well as you can also load DMS files directly in Amiga emulators too. Personally I would stick with ADF.
What version of Directory Opus is it? You should try it out. A File Manager is very useful and DOpus especially.
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Indeed, Killer Gorilla rules.
He has spent alot of time sorting these, just to help us old Miggy guys (and gals) out,
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I've visited Killer Gorilla's site a few times in the past but completely forgot about that when I posted above. That should really simplify things. 