This hurt my brain to make, follow through to pic 8. after you could add power tanks in the gaps or shield generators. depends on your needs.
http://imgur.com/StSTG39,W1V6rqo,kIzy0f6,yukF4Fs,iVtMLnR,j8IE5ZM,27V9wc8,VgLjVlH#0
EDIT: This is 6x6x6. and its pretty freaking efficient (maybe the...