Reply to Good speakers for just listening, should I??

Hi,
I'm a dj but not a producer. I use a windows notebook to find, edit and listen to my tracks.
Obviously, it doesn't have a good pair of speakers, what makes it hard to me to know which track HAS some Fat Bass and which just seems to.
I edit my tracks on Audition and Ableton, so I need some clear sound sometimes.
I'm believeing about buying a KRK Rokit 5 single speaker just to make track listening more conclusive, as I use my car speakers to do the job right now.
So, should I buy a single speaker? or two? or two + KRK subwoofer? Or KRK is too good for someone who is not producing at all?
And, my notebook is a HP-G42 (very bad one). Being a noob notebook, does it has bad quality audio at the headphone exit? or it doesnt matter on the quality of the notebook? And one more question, if I buy one or more speakers, I should just buy some adapters and I'm ready to go??
I believe you guys know a lot more than me about this hehehe I need some help

Thanks!