yes you need a line convertor and you will be all set....

you just need to find a 12v switched power for the Amp remote turn on

If your car has a power antenna, Just use a volt meter to tap into the 12V supply and your good to go. You wont have to run a wire to the fuse box up front.

I would say a new head unit is the way to go, it would have the 12v remote "on" wire built in, and RCA preouts. If you are willing to wire a amp, then a head unit is a peice of cake. If you use a converter or run your rear wires to the amp (you can get a amp that will have high level inputs where you can just solder your rear wires to a little harness, then plug right to the amp), you get some distortion. Sorry to be nit-picky but that factory stereo'* mini-amp is awful. You don't notice it'* poor sound much because it isn't too loud yet. After you amplifiy it by even a 100 RMS, you'll really be unhappy. I say spring for a new head unit, Wal-Mart has some name brand stereos, cheap. Good luck and I hope your install goes easy!

Presuming you will keep your HU and tap the rear deck speaker wires:
Almost all amps you can buy come with both high (speaker level) and low (line level) inputs. If you simply look at your amp and see that you have high (speaker level) inputs, then you won't need the $19.99 line level converter. If for some reason your amp only has low level (line level) inputs, then get the $19.99 converter.