Hi Allan,
It was a lot of fun reviewing the Inclines. Unfortunately, I haven't had a chance to listen to either the AudioEngine A5s or the Polk Heritage desktop speakers. I thus can't offer you an educated opinion on that one to tell you my impressions about the differences between the speakers. Simply from a design and spec's POV, there are a few differences that strike me:
First, the Inclines are bipolar speakers vs. the Audio Engine and the Polks. The bipolar speakers do enhances the sense of soundstage depth and breadth. If that's something you like, then you'll like the Inclines.
Second, on paper the Inclines go down into the low 40's at +/-3dB. The AudioEngine speakers are only listed as going down to 50Hz.
Third, there are connectivity differences between all the speakers. The Polk seems to have the fewest options of all. The Inclines give you lots and a sub out.
Fourth, the Inclines have a "direct" mode as indicated in the review. That may or may not be something of value.
Fifth, they all sure do look different. Aesthetics play a role
Like most well-designed speakers this may simply come down to preference and I'd encourage you to try both out in your own setup and decide on which will work best for you.