I tried v3.31 beta 6.
First I noticed a regression: MIDI sounded terrible, no matter what device I select in Windows' system configuration. But, strangely enough, when I made a CD ISO image which I mounted in Daemontools (just in case you don't know: it is a very accurate CD emulator) for a test run, and I started it with the "-cdrom" parameter from there, the MIDI music perfectly plays through the selected MIDI device. In contrary to that, using "-cdrom" running it from the harddisk has no effect on MIDI (which, I know, is pretty normal behavior. In deed, I haven't even a remote clue how running it from a CD could affect the decission of which MIDI device to use.).
And while I'm trying to use the "-cdrom" switch, I noticed another bug: The switch seems to work properly, as long, the engine is executed from my harddisk. Config, Savegames and temporary files are stored in c:\doomdata as it should be, except for tranmap.dat which is written to the current directory.
However, when I use "-cdrom" from the emulated CD drive, the config is read and used properly from c:\doomdata, but no changes are written back to it, when I exit from Eternity.exe. This works flawless on the harddisk, though.