Looking to upgrade the system in my boat. Currently have an PRV250 head unit powering 4 cheap 5 1/4" speakers.

I am looking to upgrade the existing speakers to 6 1/2" Polk DB651 and add 4 more plus add a sub.

I am looking at a JBL MA 6004 to power the 4 polks going in place of the stockers. I assume I will use the hi-power speaker leads for this amp.

I am thinking I will add another JBL MA6004 to run the 4 additional speakers. And looking at a self powered 10" 250 watt bazooka tube.

Unfortunately the head unit has one set of pre outs and the normal high power speaker leads. The JBL MA6004 has two sets of RCA inputs so on that second amp, how would I power that from one set of preamp outputs on the head unit?
And what about the Bazooka - how do I power that?

The JBL amp has a single set of RCA outputs so I am sure I can drive the sub from that. Just unsure about that second group of 4 speakers and how to generally hook everything up.