My understanding is that heat causes spandex fibers to break down. I have even read that you should not wear Speedos or jammers in the hot tub/jacuzzi because of this. So, I doubt that washing spandex in hot water is a good idea.
I would think the best soap to use is a mild one like those intended for delicate fabrics (such as Woolite, here in the states).
Some gear even suggests you wash by hand, do not dry in a dryer, and do not hang in the sunlight to dry (the UV rays will bleach the colors). So, I guess if you really want your gear to last, treat it delicately when washing.
Hope that helps!