You are NOT going to find any performance chips for your US-Spec BETA engine. They are simply not in existence. Chips are made for the other BETAs, which use MAP sensors to determine intake air volume...but US BETAs use a MAFS sensor instead, and these send out different signals that an ECU expecting a MAP out there won't know what to do with. Sorry....it sucks, I know, but it's the cold, hard reality of the situation.
MAP - Manifold Absolute Pressure; essentially a barometer. Sends the ECU the pressure currently in the manifold, which the computer uses to determine volume of air being sucked in.
MAFS - Mass Air Flow Sensor; an electrified bare wire exposed to intake air. Another sensor checks the temperature of the electrified wire. As air flows past the wire, it cools. The sensor wants to keep the wire at a constant temperature, so it flows additional current through the wire to bring it's temperature back up. The sensor tells the ECU how much current is being needed to keep the wire hot, and this is interpreted to determine how much air must be going through, trying to cool that wire.
<hr width=60% noshade size=1 align=left>Shyt, screw dis fuggin' shyt! Fuk! [makes driving-away motion] - Guilty