Can't seem to find specs for KLM AV5001 but I found KLH AV5001
http://www.amazon.com/KLH-AV5001-Flo.../dp/B000021YTH
You can use your existing speakers... if it ain't broke don't fix it.
Well, ideally it would be nice to have a matched speaker set but given that you will need to purchase an AVR for $700-800 and shell out some more for speakers, I have to ask, what's your budget?
My rule about AVR to Speakers ratio is at least 1:3, so if AVR is $800 you need at least a $2400 speaker system, higher is better.
Are you ready for that?
Otherwise you can get a mid-level speakers, buy seperately, get one for center and another 4 satellites/bookshelf/floorstanding, use your existing pair floorstand as front speaker and the subwoofer for a total of 7.1.
Another option is to call crutchfield.com advisor and tell them what you have and that you plan to upgrade the speakers with given budget constraint.
Or wait for other expert members here to respond.