Miang = Mary Elizabeth McGlynn.
She could fit Dominia too (played more forceful then creepy of course... this VA can do both well imo).
Bart original japanese VA was perfect. His english one though
... I guess a somewhat manly and energetic voice would suit him, it just needs to fit his freaking age.
BTW, what would you think if the characters were voiced by non american VA ? Make it international or something (that would add flavor to the Xenogears world in a way... Solaris has his own language, Kislev reminds me of Russia a little bit, Aveh is arabic, Aquvy... maybe british/american (Billy and his orphanage reminds me of anything Dickens, storywise... but their looks are american). Xenoblade was refreshing with its british cast... but international VA seems more interesting for a game like Xenogears.