ok, although there are benefits to a mono amp (class D) the 801d mtx amp makes its best output at 2 ohms... you can either run your sub at 1 ohm or 4 ohms, so in this case your better off with the slightly less efficient 502 class AB amp.
the 801d at 4 ohms mono makes- 250 watts by 1 channel at 12.5 volts (it is also possible to run this amp at 1 ohm mono, i've done it before, but that would provide way too much power to your sub...)
the 502 at 4 ohms mono makes- 360 watts by 1 channel at 12.5 volts
both of those ratings are a little lower than what you'll actually see since the amps are slightly underrated, and you'll be running at a higher voltage than that most of the time. In this case i'd go with the 502.