The LSR 305s have been compared favorably with the Adam F5: http://www.cnet.com/news/jbl-lsr305-resetting-sound-expectations-for-desktop-speakers/
Don't be overly focused on watts. It takes double the wattage to produce +3db more volume, and +10db is generally considered a perceived doubling in volume to the listener. So the difference between 50 to 100 watts is not as much as you might think, not to mention that amp wattage doesn't tell you much with speakers unless you know the sensitivity of the speakers, too, because volume is a factor of wattage and sensitivity. Finally, the Emotiva 4s have more than enough volume for desktop speaker use. You won't need additional volume.
Finally, the Airmotiv 4 is an acknowledged better class of speaker than the Audioengine A2. Bigger driver, better measured low end response, and it doesn't have the artificial bass hump the A2s have (the amp has been tuned to add in more upper midbass because it doesn't do lower midbass). The Airmotiv 4 is considered a competitor with the Audioengine A5 series.