As amer stated:
"Dynamic power ratings are very misleading, don't know why more companies don't give RMS values which are more representative of the true capabilites of the amp"
This is true but the dynamic power rating should not be considered an absolute value for what speakers can be used on that amp. I read dynamic power readings as the power capabilities that the amp can handle but for short bursts or spikes of a heavier load.
I still prefer to read the RMS values of an amp and i would put more confidence in running a 4 ohm speaker for an amp that is rated with 4 ohm under the RMS spec. Most of the Denon, Onkyos , etc. usually have an RMS value of 6-16ohm with all channels driven and sometimes they throw out a spec like 4 ohm (xx Watts) 2 channels driven.
They market the very limit of the amp to make it sound like the amp is capable of such a feat but again, as amer noted:
The M80 is a 5 ohm load, but there is still enough 'dynamic range' to trigger my onkyo 787 protection circutry on occasion. SO much for Onkyo's WRAT (Wide range amplifier technology)...another useless marketing gimmick."
This is why i threw our my earlier comment:
"I may not consider running a 4 ohm speaker all the time with these models but it certainly would depend on how the 4 ohm rating was assessed. If the speaker has several spikes down to 4 ohms but really averages about 5 or 6, then i probably would not be so concerned. If the speaker was more an average of 4 ohm with spikes below that, i would probably look alot closer at getting separate components."
Unfortunately i've read about amer's problem with several other people who own the 787 model. Since i have the 797 model which does not have a cooling fan, i'm guessing that Onkyo changed their heatsink or other internal components to make it a bit beefier. I've run some 4 ohm Kefs off this receiver without any problems or auto shutoffs.
All that aside, i have heard Pioneer receivers, i like them and their onboard toys and if i soley used 6-8ohm speakers i would look at them more seriously as a contender, just as i did last year.
Certainly if you already have a separate amp for your Hales, then just use the receiver as the pre-amp for processing and let the Adcom handle the power as you seemingly plan to do.
In that case, i don't think the power specs of the Pioneer would matter quite so much in your decision to purchase one.
I'm guessing you are not interested in finding a separate pre-pro and amps for surrounds eh?
