Use the same method that the dsda preamble uses to figure out what the main wad is.

dcc/eureka.py

@@ -4,16 +4,18 @@ import subprocess
 
 
 class Eureka(dcc.doom_base.WadMap):
+    def get_parser(self, prog_name):
+        parser = super().get_parser(prog_name)
+        parser.add_argument("--main")
+        return parser
+
     def take_action(self, parsed_args):
         iwad = self.iwad_path(parsed_args.wad)
         pwadpath = self.pwads.joinpath(parsed_args.wad)
-        mw = list(pwadpath.glob(
-            '*{}*.wad'.format(parsed_args.wad), case_sensitive=False
-        ))
-        if len(mw) != 1:
-            raise Exception(
-                f"Unable to guess at main pwad for wad {parsed_args.wad}."
-            )
+        if parsed_args.main is not None:
+            mw = pwadpath.joinpath(parsed_args.main)
+        else:
+            mw = sorted(list(pwadpath.glob('*.wad', case_sensitive=False)))[0]
 
         complevel = self.complevel()
         port = "vanilla"
@@ -24,5 +26,5 @@ class Eureka(dcc.doom_base.WadMap):
 
         subprocess.run(
             ["eureka"] + ["-iwad", iwad] + ["-w", parsed_args.map]
-            + ["-p", port] + [mw[0]]
+            + ["-p", port] + [mw]
         )