Hi Mahi,
Speaker sound quality does not have a direct co-relation to the number of drivers used. The design, quality of drivers, cross-over, voicing etc are a few of the parameters that play into the final sound quality that we hear. I've heard excellent single driver speakers and excellent multi-driver speakers (2, 3, 4, 5 drivers and even multi-array). The best way to judge the quality of a speaker is to listen to it - one driver, two drivers or 10 drivers, does it really matter to the listener? If you like it, who cares how many drivers it has!
Best,
APK
P.S - While I am in no way an Acoustic Portrait fanboy, I would suggest that you give it a listen before dismissing it. I have heard them, and IMO, they provide excellent value at their price point. YMMV though....