Dr,is it even worth it to put money towards the subs if he's going to put them in the enclosures that he's making? If there is no way he'll be able to put the subs in free space, I would probably go without subs and get buttkickers as CV suggested. The M80s have bass down to 34Hz, even lower in room, the buttkicker will take car of the effect.

Bruno
M80s/VP180/QS8s/EP600/AVR-890
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"The problem is choice..."