Have you considered going wireless, using portable Bluetooth speakers and smart phone or tablet. We have removed all the older stereo equipment, the associated wiring. No need to cut new holes in the cockpit or companionway bulkhead. The speakers we use are the NYNE VIBES. They have true wireless pairing, more than enough volume and can be placed wherever you desire. We typically place them in cup holders in the cockpit table. They can also be placed on the cabin top with a little help from some adhesive velcro strips. The pic below shows the red and blue speakers in front of the pedestal guard.
Our H30C only had interior hardwired speakers installed by the PO. I was glad to see the automobile style CD/FM stereo and tangled wiring leave the saloon and cabin ceiling.
We also have a subscription to Spotify, with unlimited downloads.
Similar to Warren, the speakers on my 88 28.5 are mounted under the helm seat... we don’t use them. We also use a wireless speaker connected to my cell phone that has music. I also have a small Bluetooth remote control that I use to pause/advance and change the volume on the phone so I don’t have to handle the phone all the time (and risk sending it overboard)!
There is a CD player and an old cassette player installed on the boat that I’m trying to figure out how to remove and fill in the holes...
I installed 4 exciter speakers in my S2 cockpit. One on each side seatback just batt of the cabin and on the stern either side of the rudder post. No holes required, you epoxy them on the backside of the fiberglass and they vibrate at a very high frequency to produce the sound.