I'm not a ultra fan of the series (I don't really know anything about this) but I was thinking, ¿what would happen if you fuse one of the monster capsules and one of the ultraman capsules? (Sorry for my horrible english).
You should fuse ginga and max I just created a name it is Ultraman Geed Max Galaxy I make a catchphrase too,Boukenze!Ginga! It means travel, through galaxy!