I would suggest Hondata Kpro. The weak part of the S2k drivetrain is the rear end. If you do any extensive power adders you are going to want to change the rear end to a beefier setup. Most people I have seen that have done this use the rear end from a 240sx.
I would not to the ITB thing personally, especially if you are going to do piggy back EMS.
For forced induction, go with Full-Race. Their products are amazing.
Link to a great turbo kit for a stock motor and yet it has infinite upgradability for future needs if you want more power.
http://www.full-race.com/catalog/pro...38acf11d0e6212