4000 watts with a 70 amp fuse??
lets see here...
70 amps X optimistic 14.4 volts = 1008 watts input
1008 watts X optimistic 60% efficiency = 604.8 theoretical watts.
Also use this calculator when setting the gain into the ball park area.
http://www.caraudio911.com/tutorials/GainSet/voltage.htm
Bass boost is bad...not even needed. It can be helpful SOMETIMES when used correctly. Most people use it like a "more bass" knob and clip the amp and blow subs.
run an 18 gauge wire grounding the HU chassis to the amp chassis to help eliminate any noise interference in the system.