Will be interested to hear how you get on.
I removed the resonator on the Impreza, gave a little more induction roar but didn't feel any different.
There are two schools of thought, one being the resonators are restrictive and removing them increases flow, the other that they smooth air passing through the Mass Air Flow Meter, into the plenum and thus increase flow.
Are the resonators on the 156 before or after the air filter housing? I suspect the filter and housing itself would provide a large amount of smoothing, probably the resonators are just to keep the induction noise down.