Hi Alan,
Nice to see someone else in the "PIC" business.
You may have seen my Radio Controlled MP3 player thread (
http://www.modelboatmayhem.co.uk/forum/index.php/topic,50200.0.html ) where I've used a Sparkfun MP3 Trigger (
http://www.hobbytronics.co.uk/mp3-trigger-board?keyword=MP3 ).
Obviously, mine is the different requirement of playing "Gramophone" music, but could be easily used for different boat sounds - engines, sirens, winches etc. As you can see, it has 18 programmable inputs for sound selection, play next, play previous, and volume.
In my original thread it is associated with a joystick input, but with the completion of the "Voice Command System", the PIC board has been removed and it is now directly controlled via a UART connection from the Voice Command System.
The only problem I had was with some of the music "warbling", but tracked this done to the particular MP3 tune playback rate being higher than the 192kbps. So, with the problem tracks I had to, using a downloaded MP3 quality modifier, change the rate from 230kbps, for example, to less than the 192kbps maximum.
The downside is the £36 for the board, plus extra for the microSD card and enclosure - I would imaging your devices coming in much cheaper than that.
Have you considered mounting the speaker on a "sounding" board or box to accentuate the lower frequency sounds?
I hope to be demonstrating the system at Wicksteed this weekend - voice permitting.
Ian