KT,
Speakers do not create 'hiss'. They just reproduce what is sent to them by the electronics. If you have removed the EQ and replaced the amplifiers and you still have hiss then obviously the hiss is generated upstream in the signal path or the HU has too little voltage and there is an inordinate dependency on the amplifiers' input stage to create gain. Solve this and you reduce the hiss. I would have liked to help your dealer to help you without selling you anything. You already had superior gear.

David
Earmark Marine