I'm sure this will sound very juvenile to pretty much everyone on this board, but after doing some research on the topic and not finding what i was looking for, I found this site and thought i could get the answers i'm looking for and it would be a bit more clear as to what i'm trying to do.

I have, in my boat, 4 5.25" sony speakers (1xx watt peak \ 40 wall rms) attatched to a sony HU (52x4). my problem is that it's just not loud enough while i'm driving at cruising speeds. i want to add an amp and possibly 2 more speakers. i was thinking about getting a 4 channel amp. can i use the 4 ch amp to power all 6 if the amp is capable? or should i just buy a small 400 watt amp (4 ch)? i'm not trying to be the loudest on the water, just want to hear it while driving and sound good. budget is also limited.

I would get some better marine speakers, sony's are not exactly the best speakers.

Something with high efficiency so it can get louder on less power. I know MTX makes some good marine. I'm not too experienced with marine speakers. if you do get an amplifier make sure its marine certified and the same with the speakers.