I'm no expert in how outdoor speakers work but it did get me thinking. I'll share my thoughts and the experts can correct where needed. In short, I think I agree with John in that you will be disappointed without investing heavily in a much more radical solution.
Lets say you did have the Algonquins as they are a nice outdoor speaker according to specs and reviews. How much power would you really need to get to the screaming levels you desire. Not a whole lot maybe, except you are outdoors. In the outdoors the speakers tend to point off into infinity with no walls to reflect the sound back at you and you also tend to wander further away from them at times.
OK lets put the speakers maximum peak usefulness and the eventual distortion of being pushed beyond it's specs aside. I did some wattage calculations using this online wattage calculator.
http://allegro-sound.com/Power.htmlI used 4 meters for the distance (you can adjust to your situation.) I used the Anechoic sensitivity rating for the speakers (because, I think, that would be closer to pointing away from walls. I suspect the real number is somewhere in between.) I also plugged in a tiny bit of headroom, 10db, for the peaks in the music.
---Using the above, a comfortable chatting level of sound, 75db, even with 10db peaks you are using only 8 watts.
(Note: If you were indoors, your sensitivity would change to 92 and you would need only 3 watts, even with 10db headroom, 75+10=85db))
---Bumping this up to 85 db and you are now at a fairly loud movie theater level. This is what I think of when you describe 'you have to speak up but not scream.'
Now to comfortably play at 85db + 10db peaks, you will need 80 watts. Now you have gone beyond the ability of your current 50 watt per channel amp and are creating distortion.
((NOTE: If you used an indoor rating, you will still only be using only 32 watts and you would be plenty safe. My choice to use anechoic chamber levels for the calculations are probably overkill so you are likely still OK.)
Now to get to 'Must shout to be heard levels', lets say 95db + 10 for peaks = 105db.....
Most any gear made for the indoors is going to struggle or simply fail. Calculations for this level show you would need 319 watts. Now you are talking an ultra-powerful and equally expensive amp and you will need to upgrade your speakers to M80s to be able to handle that much power.
Now a better guess is needed on what sensitivity range is needed to replicate your exact outdoor environment and distance but also consider that I only allowed for 10db overhead where realistically, to be safe, that number should have been 15 or maybe even 20 if you enjoy classical or other forms of music where there are a lot of dynamic volume changes within the music itself.
I'm sure John or someone can fill in the blanks and assumptions I have made but it's worth thinking about before you spend a lot of money.
