starting at the end, stepper motors, particularly when stationary, get hot.. often too hot to touch (that's about 65degC). If you are concerned get a digital temp probe from Maplins for £19.99 (doubles as a test meter so useful to have). remember when stationary one or more coils are permanently energised.
Having said that, it is important that the stepper driver has the current limit set correctly for the motor in use - too high and it will overheat the motor leading to coil burnout and/or demagnetisation of the magnets through heat.
I don't know which Kemo controller you refer to, is it the M106? If so then for a 6.8v motor you need a power supply of +/- 9v approx maximum as the M106 needs a split supply. Also the M106 does not appear to have any form of current limit or chopper capability, so you need to keep the volts to about 1V above the motor rating to limit the current. If you are thinking of using a 12v supply (presumably the +12v and -12v rails from an ATX unit) you will need a dropper resistor of 5.6ohm rated at 10W in each supply line otherwise your motor will overheat - 2 off Maplin's part # H5R6 @ 40p each will do, but mount them on a few sq cm of aluminium as a heatsink as they will get warm.. Unfortunately the Kemo controller is just too simplistic for real prolonged usage as it has no protection circuits or control capability - all too easy to fry if you are not careful.
Whereabouts in UK are you?