I don't know about the placement. Hopefully Craigsub will read this and offer some suggestions. But, as far as "how much bass is too much," there is a very nice fellow (Frank Manrique) who posts over at the Home Theater Forum, who has 8 (count 'em EIGHT) SVS 16-46 cylinder subs, and 2 (count 'em, TWO) SVS B$+ subs. Then there is Craig himself, who has just one or two measly subs (see here).

Jack

"People generally quarrel because they cannot argue." - G. K. Chesterton