Depends on your budget.
Quality 5-6 channel amps can be steep. I personally run two. 200w Kenwood to doors and 250w MTX to the sub. Total cost about $350. I set the amp for my doors to high pass and the sub amp to low pass, very clean at high volumes.
A friend of mine had a 5 channel amp that was like 1000w (probably about 600rms). Don't know how much he paid but it started acting up after a couple months, would shutdown after about a half hour. In his case the two amp set up would probably have lasted longer than the one because he was pushing it at capacity all the time.
