OK, now, inside or outside?
I was discussing inside, which is where most people start. Our C25 only had inside speakers, so we had to crank them up and turn them down when we went below. Never did put in cockpit speakers.
Cockpit? Drill holes in your vertical fiberglass under the helmsman's seat or mount speakers externally.
Equipment? Automotive has been "deemed" suitable from almost everyone on this Message Board. There was a topic just this week about it. Switch your new posts to 5 days and look around, or do a search on the word stereo and read the last five years of good stuff. Equipment also includes remote controls. Depends on how adept your crew is at sail handling and volume, level, equalization and faders at the same time.

Location for receiver: I have NO idea what your layout is. I'm fortunate that I know a bit about a C27 -- do you have the traditional of dinette layout? Where do you sit? How far is your wiring? What do you like to keep on your shelves? You could mount it over your hanging locker across from the head, but you may have stuff there. If a dinette, would you like it close to your seats, or if you buy a remote, across the saloon could be just fine. Joe, you gotta personalize this to your satisfaction.
Funny things about boats -- would you ask someone where to put the stereo in your house? Just askin'...
