This truly-designed-for-boats stereo was nearly new when I bought Gizmo in 2009 and it really impressed me over the year I used it (before storing it to test other models). The small main and remote control heads are easy to use and easy to mount most anywhere. They include separate volume control for the two amplified speaker zones and a simple one-button intercom feature. They can also function like two separate stereos when using the zone 2 amp's "aux-in" source. The CD player/radio/amp, which can be mounted in a cabinet, has two aux-in ports, and it would be easy to turn any of the aux ports into a Bluetooth source using a self-powered receiver like this:

https://www.amazon.com/gp/product/B01MXF6HFS/

Manuals for the MRD-70 AM/FM Radio & CD player, RD44 control heads, MZ-100 zone 2 amp, RT-20 network router, and IXM-10 XM interface are still available at Poly-Planar, along with some system components at clearance prices. (Buying new makes sense now if you don't need two zones with intercom.)

https://www.polyplanar.com/documentation/

Note that I recently checked that everything works except for the included XM radio, which may be obsolete anyway.

$200 plus shipping for a system that was ahead of its time and has only been used about 3 boating seasons. Don't hesitate if you have questions.