Not quite sure what you mean by "undub," but do be aware that the Japanese version of every game is included and ZX Advent, if you play that version, does include the original Japanese voice track. So if you know your way through the game or are willing to use a guide (or just know Japanese), you can play ZX Advent with 100% less booty.
Still, as bad as the English voice track is, it's charming as hell in that amateur-as-hell, what-were-they-thinking sort of way... minus the offensive stereotypes like Buckfire and Rospark, but what can you do.
Also, for what it's worth, the Japanese version of each Zero game restores the blood spurts, too.