Mike,
The boat came with an older Sony, I'm sure it has AUX-IN, but in all honesty, the owner is kind of like me, would rather hear the water lapping on the hull or the engines purring than listening to music, thus a stereo upgrage was not in the equation. So with the Sonic hub, everything is controlled by the HDS-10, plus it has the Ipod dock and, besides me, nobody listens to CDs anymore, so the stereo up top is almost moot.
But I figured there was another way to do this, despite what Glen E and Birdman told me...
In reality, the Sirius module is there for the weather...