Warrj,
You misunderstand me - I'm not suggesting the Nautilus 805s aren't good value. I think they are, extremely good. But the fact remains that they are speakers which cost £1400 for the pair, and it would be unrealistic to expect them to sound as good, say Nautilus 803s at £3500 for the pair.
In terms of comparing costs people usually say that for a stereo system you should aim to spend very roughly the same on the pre-amp and power-amp combined as you do on the (two) speakers. For a home cinema setup you should aim to spend about the same on the processor and power-amp combined as you do on the front three speakers - so when you factor in the surround and subwoofer channels the speakers work out a lot more expensive. Working out the price per channel is simply misleading in that particular context, doubly so if you only consider the power amp part of the equation.
Two specific experiences that I've had:
1) Listened to a Pioneer AX10 hooked into Sonus Faber "Home" speakers (centre channel not to my liking but the left and right fronts at £1700 the pair in a similar class to the 805s). I was able to compare this to the same speaker system hooked into a Merdian 568 plus Krell Showcase power amp a week later, listening to the same source material (same DVD player too - Meridian 596). The Meridian and Krell combination didn't sound much better despite costing £9000 rather than £2700.
2) Listening to Arcam AV8/P7 hooked into Nautilus 805/HTM2, then switching up (after just a couple of minutes) to 803/HTM1. The improvement in quality there was truly dramatic.
I've also listened to the 805s with a Denon A1SR, although rather longer ago.
Put it this way: if my system consisted of either the Denon or Pioneer plus 805/HTM2/SCM1 speakers and I had the chance to upgrade either the speakers or the processor/amp but not both, then I would upgrade the speakers.
I'm not quite sure what you mean by a "difficult" load. If you're worried about overstretching the amp in power output terms then I wouldn't be. The Denon, for example, is rated at 170W per channel into 8 ohms rising to an impressive 310W per channel into 4 ohms.
Obviously much of what I am saying here is, by definition, subjective. To my ears the effect of the 805 speakers on the quality of the sound is marginally more irritating than the effect of the Pioneer or Denon device - to your ears the reverse may very well be true. All I'm really saying is that I think you should audition Pioener and Denon devices and see what you think. They may surprise you.