The 876 has power by the truck load. It will rock any speaker you hook up to it. Where to start is somewhat of a tough question. (thus the purpose of the post I guess) I might tend to agree with Tom67 on upgrading the center first. I'm not all that familiar with the KG series but most likely any substantial upgrade you do will likely dwarf another component. For example if you up the center to say an RC-62 it will be stepping all over the KG's where if you up the towers to something like RF-62's the synergy center will just disappear.
I would definitely start up front and work your way to upgrading the surrounds and sub last. IMHO
One thought though is that klipsch speakers are generally as good today as the day you first bought them. They don't go bad and across the baord speaker tech has had to many big advances in a while. Go join the forums over at the klipsch site
www.forums.klipsch.com i think and talk to thoes guys and find out how thoes KG towers stack up to the new Icon and Reference lines. They might still be great speakers with no need to change. Some of the best speakers today are still some of Klipsch K-horns from the 60's.
I've got an 876 running RF-82's, RC-64, RS-62's (surround), RB-61's (rear) and an RSW10. So I'm a little biased.
