50x4 is the RMS of the HU. It is measured in watts only. the peak power will be in higher numbers. AFAIK
the maximum capacity of the HU is 55 or 60 watts X 4 channels only.
If you for the amplifiers they may go up to 1000watts( 250x4)
There are no such HU comes with 70x4, 80x4 or so.