If there are speakers that could use external amplification are Axiom towers. It seems one of the design goals that went into the towers like the M60 and M80 were power handling and the ability to play extremely clean at very high SPL levels and consume large amounts of power to fill large rooms.
Now if you have a large room and your listening/seating position is far away then external amplification can be beneficial. If you run your speakers full range you might find external amplification to be beneficial. The M60 and M80's will dip into the 4 ohm region full range and at VERY HIGH SPL these speakers might shut down some receivers and even some amps (M80s). If you have a small to medium sized room and sit 8-15 feet away for example I see no point in external amplification. The sensitivity of Axioms are above average in the high 80's so this is why receivers usually work for most rooms because they are easy to drive and in most cases not pushing them past their limits.
The one thing Michael_D pointed out is that some of the more expensive amps can handle even 2-4 ohm speakers to unclippable levels with any speakers without shutting down even with the most demanding of source material. The Axiom amp is an example of that. With the emotiva amps on the other hand I would limit them to 4-5 ohm speakers and up. Upgraditis is always happening. With a quality amp, it doesn't lose it feature set like pre-pros and receivers and should last a really long time from a reliability standpoint.
