AirPlay audio sync issue

I'm using AirPlay to stream audio over WiFi from iTunes 10.1 to both an Airport Express and a 2nd gen Apple TV. My network setup has a DSL modem connected to an older (Buffalo) WiFi base station, with the Airport Express connected as a WDS remote. Both the MacBook serving audio via iTunes and the Apple TV get their wireless connection via the Airport Express, which is about 35 feet away. Signal strength as seen on the Macbook is good (5 bars).

If I play audio simultaneously through the speakers connected to the Airport Express and the computer speakers, there is good synchronization. However, the audio played through the AppleTV is delayed by several (10s of?) milliseconds, which means that playing through AppleTV and computer in the same room results in a significant echo effect. The same is heard when playing through the AppleTV and Airport Express at the same time.

Has anyone else had this problem playing from iTunes through the AppleTV? Any suggestions as to how to solve this, or will it require another software update? My understanding was that AirPlay was meant to synchronize audio played through multiple speakers - this is not the case with my setup. Music played in two rooms is difficult to listen to when between the two sets of speakers.

Chris