Hey and welcome!
Here's another approach which might suit your needs.
Your 787 has pre-amp outputs.
If you have a way to verify that the pre-amp section still works, you could get one of these for $725 shipped:
http://emotiva.com/upa7.shtm
It is a better amp than what is in the 5008 (despite the specifications), and you can spend the extra money on getting the Klipsh's you want.
Of course you may want the up to date features of the 5008 and what type of wholesale price you get is a factor.
I just have a tough time with sinking so much money in a HT receiver when it will become obsolete in 5-7 years. The amp will be a gem for decades.
In truth, if yours are typical Klipsh speakers, you really don't need lots of power. They are efficient speakers.