Hardly perfect applies to any wireless network transmission. The router itself (and its location), sources of interference (neighbor's WiFi, other 2.4GHz home devices) and the number and construction of walls and floors the signal has to pass through are all significant variables.
In my home, with my router (Netgear WNDR3700) and 3 Airport Express, reception is perfect either with iTunes or with other applications running through Airfoil.
The Audioengine D2 ($600) uses the 2.4MHz band and is subject to the same interference, but monitors audio quality and will change channels if the error rate is too high. It also will not be affected by the main WiFi network usage. Audioengine claims > 100 ft. range although some reviews have found 60 ft. to 70 ft. is probably what to expect from real world usage. I would also guess that the DAC in the D2 might be a bit better than the DAC in the Airport Express. The D2 can also stream 24/96 (Airport Express is limited to 16/48), if you want to stream higher res downloads in addition to Spotify.
Steve