I am installing a Jensen MCD 6115, and two Jensen power 760 amps in my boat. The reciever has output of 200 watts ( 50 x 4 ). After I hook up amps through rca preamps at reciever does that reciever 200 watts transfer through the amp? or can I still use those reciever speaker leads for 50 x 4?

no, the 200 watts does not transfer to the amp. The RCA outputs on the deck are low level outputs. They only have an actual few tenths of a watt going through them. The speaker leads, however, are the high level outputs and have the 50 x 4 rating, which is a max rating. They're actually about 20 watts RMS each. But yes you can use the RCAs to send a signal to an external amplifier and also use the speaker leads to power speakers directly from the deck.