This tuning box you speak of kind of sounds like these resistor type devices that some nut jobs fit to there MAP sensor or whatever to trick the car into thinking there is more air coming in so adds more fuel. They will screw up your emissions and your engine would no doubt lose power and perform worse. I hope this isn't what you've saw for the 1.6, I'd always thought tuning boxes were turbo diesel thing anyway?
One ex member - Danny Mercer - had the 1.6, he had some engine work carried out which increased the output to 130 something bhp, he said it was rapid and the top speed went off the clocks. It's what you're willing to do that counts, for any decent gains with NA you need more than a remap