it's already been said...if you mix with your PC speakers to the degree you want the bass sounding as your hear it in a HI-FI equipment...you'll probably end up with a crappy mix that ONLY sounds good through your pc speakers. if you take that same mix to another place where the natural EQ of the speakers favours the low frequencies you'll have a ton of mud...
good speakers/monitors help keeping the natural EQ flat, and thus, they let you tweak your mix in a more precise way to get a well balanced mix.
good speakers/monitors help keeping the natural EQ flat, and thus, they let you tweak your mix in a more precise way to get a well balanced mix.