The "extra chip" ECUs (blitz, Gforce, etc) do nothing to the fuel maps. They generally remove the speed limiter on JDM ECUs, increase the rev limiter, increase or remove fuel cut, and in some cases run more timing (similar to a JDM ECU). ALL Toyota FI ECUs run pig rich, and for good reason.
Lowering your base fuel pressure is an amazingly bad idea. Use a full standalone, or some sort of programmable piggyback that can properly control fuel independent of timing.
I use a MapECU2, works great. And yes, the MR2 3S wiring is fairly accurate. The pin locations are different across years, but so long as you tap the right wires, you're fine. Do not use the internal MAP, it's junk and running a vacuum line through the firewall is a kluge. Get an AEM or GM 5-bar and run it in the engine bay, with a dedicated pickup off the manifold.