happymatch
Leaving Skid Marks
It most certainly is. If the factory head unit has RCA outputs, then it will be pretty straight forward to wire up an amp.
Given the age of the Galant / Legnum, I'm guessing that the factory head unit does not have RCA outputs so you will need a line out converter in order to connect an amp.
Any half decent audio shop can do this install.
If you are getting an amp, make sure you get one that is rated at least 50 watts RMS not 50 watts peak power. The RMS rating is basically the power that it can provide all day, every day whereas the peak rating is only what it can produce for a fraction of the time and in limited operating circumstances.
As you are not using a sub, all you need is a 2 channel amp rated at least 50 watts rms per channel. It's pretty easy to get something decent for under $100.
When you are negotiating the purchase of the front splits, rear co-axials and amp, bargain hard! Get them to do a package deal for you or ask them to throw in the co-axials for free.
+1 for that
depending on how much you spend and research, you might find an amp with speaker level input - mine does, both 4ch and mono-. some brands like alpine used to have them, not sure they still do. If you can afford little bit more, make sure you buy the amp that can run plenty of power to it. if you under power the amp and raise the level, you might shorten the life of the speakers. two reasons. 1 there would be ac/dc frequency jumps and it will force speakers to move in funny ways. Second, id there are distortion, the sound frequency pattern would be much "rougher" and will caouse stress on your speakers, especially mid ranges and the subs. Remember dimi, i still have a sub to give away.
DO NOT get something too cheap~
Dimi, you might ask why some manufactureres put max out put as lke '2000 w" and all that but pretty cheap. I do not think there are any shop sells the amp which says peak of 50w... anyway, well, they are not really bulls*#ting. They sometimes shortens the pulse of the output. like "beeeeeeeeep" to "beep" and produce really high impacted output but lasts about a millisecond. RMS is more like continuose. so do not get confused.
I used Audiolines, Alpines, JVC, Kenwood so far and was happy with them all. Good luck with your shopping