Have you checked the Tacx user forum? Might be some information there and if not, I'd contact tech support directly. There likely is a software calibration procedure though they might have to send it to you. I ran into this issue when I reviewed an Elite Realpower trainer last year and the display was much more accurate after the calibration.
To note, though, I'm just wrapping up a test of the Bushido right now. When the tire is properly inflated, the displayed power is surprisingly accurate as compared to a reference Powertap hub.
The Bushido doesn't use a standard screw-type setup for the rear roller pressure. There's a quick-release lever and the the pressure is pre-set. Any adjustments to the displayed power will have to be done in the software aside from any variance in the tire pressure.