I guess in the literal reading of below, there isn't much of a structural issue in carving out circles. Just questionable motivation
I can make the speakers watertight by building out a small speaker box that juts into the laz (it's actually right below where the side lockers would be) with one side of it against the hull. I've been on PS#1 and was impressed with the sound. And it is a good point about dunnage blocking the speaker. The issue (for me) with where the KLH speakers are is I can envision a scenario where I jam something aft and break the speakers off! So that's how the bulkhead mount idea came to be.
The deck plates, I know, have questionable value. Maybe most days, it won't matter. But I know me - the day I'm huddled in the cabin, waiting out a storm, and want something out of the laz, is the day I'll regret not putting in the deck plates. They're easy and cheap to install. If PS#1 has any drawbacks, and this is true of any smaller boat, it lacks "away" cabin storage. Stuff gets stored out and about or in duffel bags in view. So having access to the laz, at least mentally for me, opens up some cabin storage possibilities.
Dana: I vote luddite
There are times when the sound of the wind and waves is all you need, and there are times when you wanna rock. Plus with people on board, expectations of what it means to be sailing changes, too. Now, I'm not one to cater to passengers, but music is a reasonable request. So is wine. I can't imagine not having a radio; then again all you really need is a smart phone and Pandora.