According to Twice Harman Kardon is readying an AirPlay module that will connect to their current A/V receivers and future AVR’s. The module will allow you to stream music wirelessly over WiFi from your iOS device and your computer via iTunes. It’s expected to rollout in a couple of months. Price is unknown.
I’d be curious to see how this module works since many people have requested some sort of AirPlay dongle or module that they can plug into a set of powered speakers or a receiver. My guess is it’s only going to work with Harman Kardon products but it would be good if it could be plugged into any device and costs less than an AirPort Express.