[JP78]

Since you're using a Mac source you can use a pair of Audioengine A5's being fed input by an Airport Express...total cost $449 (or $549 in bamboo).

[Christof]

My mom has a pair of these and I really like them...
How would I use 4 of them with an AE for signal?

[srb]

Using a single Airport Express would require way too long of a line out cable going to the other side of the room, and I don't know how the Audioengine's inputs would react to being paralleled with a Y-cable as well.
 
The solution would be to use two Airport Express, one at each speaker connected with the included 6" line cable.
 
Airport Express can be regularly sourced new or like new on eBay for ~$50.
 
Note: I assume you are going to send stereo to each pair of speakers.  I mention this because the current AE wireless 'N' version will distort badly if the line output is passively summed to mono, whereas the previous AE wireless 'G' version worked fine in that mode.
 
Steve

[funkmonkey]

You could try Audioengine's W1 wireless dongles (send & receive) to link the two pairs for another $99.

I have a pair of the A5s and they are the reason that I upgraded my "big" stereo.  I wanted it to sound better than the A5s