Dumb Question

I have an HK AVR 85 that had been used for 2 channel system.
I have been trying to create a HT system on budget and need some advice. I have two B&W Nautilus 805 for front, just got a ASW675 (have not hooked up yet), a small Infinity for center channel and some old speakers for rear.
Problem is, with my current set up, even without the Sub, I can barely hear the sound out of the rears.
I am totally at a loss on how to add to the power of the HK.
Can you guys recommend any amplifier that would complement the Harman Kardon AVR85?
I would like to go for a 7.1 reciever in the future...but not immediately.
Thank you.
Regards