Having done this successfully on my Hartley cabin boat, I thought (at Martins, suggestion) I would put a few bits of info here to make it simple (and it is) If you can pair a BT speaker or similar with your phone, it should be no problem setting the music or radio from that medium.
You can use a Micro SD card with pre-installed music, (uses the remote) or plug the board into your computer and download to the card, - or play music from your computer through the board (or perhaps by BT from your computer to your boat - at a show maybe) I use a 1s 200mAh LiPo to power mine which is quite adequate if the music is recorded at a decent level ( the higher the recorded level the louder the volume available) - it's only 3W without an amp but loud enough to annoy the fun Nazis😁
I started with good 3W 4 Ohm speakers which worked well in a boom box (plastic jar) but took a bit much power to drive, and were a bit heavy (ok in a 40" boat with more room). I then changed to cheap 4 Ohm .25W speakers, and these gave plenty of volume but are a bit sharp (even in the mini boxes I made for them), but again, that can depend on the quality of the recording. The pictures should give a good idea of what goes where. Speaker wires should be copied to each set of terminals (+ and - of each speaker to each of the L+R terminals ) to keep the speakers in phase ( see pic -don't cross them between sets of terminals)
For the BT radio side, I use a Ruizu BT player which is an amazing little bit of kit. It can play from a Micro SD card, play radio (even has an auto search and station store) has an earphone jack which can be used as an aerial socket for an external aerial on the boat (see my set-up in the recent Hartley blog) has a voice recorder and a number of other features in a tiny package, (around $30 NZ)
I have mine strapped out of sight under the cabin roof, and connected to the external aerial as the radio, and it works well. It can also be used externally as a BT player (card) or remote radio when paired to the board, so you can change stations, music etc on the go in your boat. Also works with BT speakers.
All Items available on Ali Express (the cheap speakers I bought from my local electronics store for $5 ea)