I have this one and I used to have the smaller Audioengines, the A2.
I though the A2s had a somewhat more balanced sound but distorted more and I prefer the Aego M. They certainly have weaknesses as well, due to the small satellites. These may be more exposed with some types of music than others. They play loud and the size of the room is not a big problem although they would benefit from a small to medium size room.
I do think overall that 2.1 systems with small satellites are not ideal for music but perform noticeably better with movies.
I think the A5s should be the best of the three and shouldn't have the distortion problem of the A2 as they would play louder anyway.
An advantage of the Audioengines is that they have twin inputs so you can plug your Squeezebox and your TV if you don't have a 5.1.
All 3 systems will have a very big advantage over the standard TV sound.