A Sensi challenge could be anything, really. Win a competition such as the World Cup with a really poor team; play as Team A and beat Team B by the highest margin; score from as far from goal as you can; score goals with every player in the team; score as many goals as you can by dribbling the length of the pitch with the keeper; try to get as high a percentage of possession as you can - there are loads of possibilities. A similar thing is often part of console football games, with preset scenarios of varying difficulty to complete.
Re Amiga controllers on PC: I also use PPJoy, but in conjunction with an Amiga 4-player parallel adaptor. It works great. The adaptor was originally bought for my A1200, and is still used on it when a few mates want a game of Air Taxi or whatever on The Real Thing. Vesalia
advertise them at 3 euros (about 2 quid).