Amplifier Help

[4TA23]

Ok I am currently running an Onkyo 805 and my front speakers are JBL Northridge E-80's (see pic). In a discussion with a sales person from BB (seemed to know what the heck he was talking about, but who knows, that's why I am here) he said that running a three way speaker as my fronts off the 805 I would not be able to fully power them and get as good as sound as I could get and I should add an amp to the system. Now when it comes to anything past a reciever I am clueless. I would not want to spend a crap load of money on one either but something decent. Do amps for HT work like car amps??? run everything to reciever, have preouts on back and run to channels on an amp and hook speakers to the amp??? Then I get extra power sent to my fronts???? If so do all I need is a 2 channel amp??? HELLPPPPP!!!!!!! So very cornfused... just want the best sound I can get. If you need more info on my system let me know.