BlackAura the great coder behind the excellent Doom Port for Dreamcast called NX Doom, has posted this news about the new beta released tonight:

New features include:
Fixed support for Final Doom
Fixed Doom skymaps
Fixed Doom 2 -warp command
New WAD loader
More compatable
Loads mods a bit faster
More DeHacked stuff
MOD music
Sound volume fixed, and soundsystem improved
Sounds compressed, so downsampling is unnecessary
Changed controls, so you can now select Nightmare mode

To hear music, you need to download a music pack. We currently have packs for Doom 1, Doom 2 and TNT Evilution. Just unzip them to the same place that the Doom WADs are stored, and nxDoom will load them automatically

The NX Doom site is HERE