Receiver or Amplifier?

I currently have an older Harmon Kardon AVR-80 receiver (5.1 - 85 watts per channel) and Miller & Kriesel speakers and subwoofer (S-150THX, SS-150THX, MX-350THX). As the model numbers suggest, both the receiver and speakers are THX certified. My room is large at 13.5 x 30.

I have been pretty happy with the sound quality over the years, other than I would like more sound/effects from the rear surround speakers (not sure if the deficiency is my system or the DVD technology?). However. my receiver is going kaputs (i.e., no display lights and shutting itself off).

After doing some mid-range reciever research, I am starting to wonder if I will be happy with just a receiver, considering my room size and that the M&K speakers are 4-ohms, or do I need to bite the bullet with a lesser wattage receiver powered by a separate amplifier. My initial research suggests my pocket book would take a significant hit going this separates way!? Any input on this subject would be appreciated!

Speaking of Harmon Kardon, they seem to be MIA as far as the mid-range receivers. All my research has revealed is low end and high end units. Am I missing some units?

Thus far, the stand-alone receivers I have been considering are as follows: Onkyo TX-SR-806 (concerned by the reports of how hot this unit runs?), Sony STR-DA5300ES, and the Denon AVR-3808CI.

Thanks in advance guys and/or gals! Merry X-mas!