I can answer this since I have been working with Signature for my valve cover to have this done to it. Cres, feel free to jump in if I am off base.
The valve cover was designed to handle the stock horsepower output levels of the 626, Protege, 323, MSP and so on. Even though they all have different power, they all have the same size passages in the valve cover baffle system. Turbo cars will produce more blow-by in nature due to many factors such as lower compression ratio, more pressure in combustion chamber, higher RPM average driving, less vacuum while accelerating and so on...
There are 2 passages for the crankcase to relieve its pressure; the PCV port (upper crankcase) and the side vent (lower crankcase). When the PCV is forced shut during acceleration, the pressure will relieve out the side vent fitting of the VC. Brian's catch cans/ PCV eliminator kit works the same way as stock, except the check valve is spring loaded instead of relying on gravity) The check valve is also located AFTER the crud is caught. This means the check valve will STAY reliable since it doesnt get gunked up like the PCV does. So no matter what PCV you use, like the Millenia S, it will still not be as reliable because the oil and sludge is still not allowing that little ball to properly seat and close off the passage. This puts the side vent into overtime trying to keep up with all that air flowing thru the tiny passages. Thats also why you will start seeing the oil in your intercooler pipes (probably rough idle too).
As pretty much all turbo owners already know, your octane rating is VERY important. The difference between 89 octane and 91 octane could mean the difference of detonation or not. Those few drops of oil are doing the same thing to your octane, bringing it down. And sometimes its more than others depending on engine temp and driving habits so your fuel is also inconsistent because of this as well.
So long story summarized, Brian is going to machine the internal passages to allow more flow. The balance from upper and lower case pressures are maintained thru the design of the catch cans. The PCV eliminator fitting he uses is not an off the shelf item, but can be done with the right products if you are DIY. He can walk you thru it if you ask him. I chose to have mine done since he was going to powder coat, and modify the s*** out of it anyway.
I will be talking with him thru the whole process. Let me know if you have any questions and I can ask him at the same time.