Karlis,
Thanks for this idea. I've been out of touch with the HiFi world since I became a boat-dweller, and hadn't heard about these amplifiers.
Doing some research, it seems that it would indeed be a very good way to go. The most suitable one for boat use that I can find is the
Temple Audio Bantam 'Classic'. It works on 12v supply, its quiescent current draw is only <60mA and its maximum current draw is 1A (compared to my cheap car radio, which draws half an amp from zero volume up to my usual listening level, and then much more above that). Independent reviews rate it very highly.
It seems that iPhone/iPod/iPad devices send out a very high quality signal from their headphone socket. Connected to one of these amplifiers and then to a pair of high quality car speakers, you will get the best sound that you can expect to get, aboard a boat with limited space and limited power supply.
I'm tempted. Since I went out of range of BBC Radio Three and Four, I've found very little to listen to on the radio, and mostly I play CDs. I have a drawer full of 200+ CDs, all of which are backed up on my computer and iPad, because they are vulnerable to damage. When the ship's batteries are low, I listen to music on my iPad with good headphones, but I'd rather listen on my pair of Alpine DDDrive speakers. So if I got a Bantam amplifier to place between the iPad and the speakers, I'd have a high quality, low current draw sound system. And I could put my CD collection into storage.