As far as i can see from the images in the site, the system makes a very coarse activity cerebral measure. I mean, to do a complete brain mapping (involving all the brain areas) you need around 24 sensors and some of them are far away of the game head bands.
Is important to note that in a real brain map, the heart beat is not taked in account at all, just the very low frequency waves ( under 100 Hz) around the cerebral cortex.
So... i can imagine that the bands are taking in account just the frontal lobe (Higher cerebral conscient activity) btw the one damaged in most of the serial killers
. If i'm not wrong, this area controls some body movements as well (the eyes following a light, the tongue and so on) but not shure.
then...you can start to create a low pass filter and a very good aplification and see it with an oscilloscope, use some "volunteers" (aka family, lol ) with diverse stress, anger, happyness, etc levels, move the electrods around the frontal area to get the right spot ( use special gel to make a good contact with skin), then you can choose the game "rules" since they are a bit arbitrary and depends of what one choose to take in account, isolate the "good waves" and then you have the tip of the iceberg.
Just a humble input about this interesting project.