Also I would take that THX certification with a grain of salt...
Just because it says THX doesn't mean when you are all done setting it all up, that it will be THX certified... It gets much deeper then just buying the components that say THX... Layouts, sound measurements, perfect speaker placement, crossovers... and on and on... From my reading and research you should just worry about what sounds good to you...
I think you should be thinking about seperates for that speaker setup, as I would imagine they will require some good quality horsepower, but thats just me... I personally would find a different speaker setup.
Use a lesser priced receiver as a prepro and a good amp.
You can make tradeoffs here and there.... and still achieve the same output.
I spent 12K on my setup... and it sounds awesome to me, my receiver and amp both say THX but I honestly could give a dump about that.. I could have painted that on with a crayon, just to say it says THX.
Don't forget to keep some acoustic room treatments in a budget as well.
Good Luck
Warp[