My guess is that it would be "better" for two reasons. One that there might be the possibility that it could turn the device on and alter the volume as opposed to simply selecting tracks. The other is (and I'm making an assumption here) that you wouldn't have to use the abismal DAC in the Airport Express, but rather the very good and expensive one that you've presumably paid for if you're using a BeoSound 5.
That being said, it would be less useful unless your Active & Passive Kits also had AirPlay.
Trip, Does this mean that a lot of your customers are asking for Airplay? Do they walk out when you say Airplay is not supported. Is there a big demand for Apple's hobby, Apple TV to be built into Beovision TVs? I buy Apple products knowing they will be obsolete in less than 3 to 5 years. I expect to have my Bang & Olufsen purchases somewhat longer.