The premium speaker system (with stock amp) has some very nice speakers. They can handle a 400wrms amp and put out level sound with some decent subs.

I just installed a 400.4 off the stock HU using the stock line outs and it was a decent sounding system. The highs were clean and defined but not too bright, the lows were noticably robust but they didn't turn out of phase with the subs like a lot of mids will do without a crossover.