Cheap marine speakers. Need amp?

I feel like beating a dead horse when bringing up any boat stereo related, but anyway - I'll give it a shot since everyone's talking about 10k systems.

The marine speakers I've been looking at are delived by Watski - a boat supply company in Scandinavia. They are coaxial 6", 80W. Frequency 60-22000 Hz.

I have no clue about stereo and hifi, but I do know loud music when I hear it. I'm considering four of these. I have a Sony MD player wich has a 4x60 watt amp. Will this do, or should I consider another amp. Will I need a marine amp, and if I'm not buying an amp, will the head unit be able to play at max volume for a long time without taking damage? Will the sound be really bad when playing at max volume?

I appreciate all replies, as long as they're not insulting me or my family.

PS. I'm on a tight budget here. These speakers are $70 each. I'm not planning to spend more than $350 on the whole system.