Are you looking to buy one? If they are the same price I would go with the Marantz MA500. It is specked out at 125 watts into an 8 ohm load or 180 watts into a 4 ohm load with harmonic distortion at .05% and intermodulation distortion is .008%. Another key element is the damping factor, which is 200. That has to deal with how well it controls the cone movement( or there abouts )Another added bonus is it is THX certified so you know it's quality.
The PE 250 "says" it has more power but.... it has more distortion and who knows what the damping factor is. Don't get me wrong, this is for a sub so it doesn't have to tube amp sound quality.
A ton of people have used the PE 250 amp and love it so it's no P.O.S. either.
Hope this helps.