Perhaps there's room in the gunnel/coaming like we did in the 208:
In the helm area I used box speakers mounted to the hull liner:
Put a subwoofer on the port side, mounted in the seat base housing:
The head unit is a Sony marine, AM/FM CD, MP3, with a Bazooka 600watt amp that drives the sub. Sound output is fantastic - have about $500 in parts in it.
I had a whole DIY written up on this but I guess the forum doesn't keep the old threads. They must be deleted after a time.