I could succesfully start Sigil using DoomAttack-AIO by modifying the DoomU (Ultimate Doom) launch script:
Code:
DoomAttack -wad $MainWAD -file SIGIL_COMPAT.wad -fps -joypad -noinputhack
I had no luck with the original DOOM.wad because it was missing a texture.
Also no luck with SIGIL.wad and DOOMU.wad - Sigil splash screen is OK but the fifth episode didn't show up.
Haven't tried on real hardware yet, but you'll need a beefy Amiga to play this with acceptable fps (040+ is my guess).
update: eh, quits after a few seconds with "Error: R_FindPlane: No more visplanes". So DoomAttack isn't one of those ports that have this limit removed.