If you're up for some experimenting, look into a divided turbine housing; running each cylinder bank to a separate side.
http://i.imgur.com/DGKY3rz.jpg
There are a decent amount of high flowing T3 inlet flange style turbos out there, but maybe there's a divided T4 housing out there that won't break the bank. Note: You'll have to run a split wastegate setup like:
http://i41.tinypic.com/2011yx0.jpg