You can connect the side port of the WG to the existing lines and that's it.
like the above comment stated you should run 1 bar. But if you want to control the boost you will at least need a boost controller and the fastest cheapest way is the manual boost controller. However, you will have to know what to disconnect and where to plug the MBC. Also, you probably will have the throttle body shut down around 1.25 bars... especially since I know GIac has the 1.3 bar safety in it. I had the same set up and it only worked after e diode was installed into the mother board. This is a headache I would not go there.
I know for a fact now that the reason ur car drops boost is that the its the ECU... your overboosting with set up and the ecu is doing it's job- preventing it from letting you blow up the car.
I would STOP doing what your doing and let a professional do the work... BTW, the headers and externals are totally unwarranted for your application.
Sell the headers and the WGs and put back what you originally had...
This is just my honest opinion.... and the reason I told you to even do the MBC is because you will probably screw up the EBC which requires a more detailed hook up.

Bottom line= if the car will not run well at 1 bar and NOT overboost once you hook up the side port of the WG to the existing lines hanging down then I would stop.