The S303 has the same issue. If you need to have volume control, you will need a network player which also acts as a pre-amp, or you will need an actual pre-amp so you have volume control.
Geez, took me way too long to find this...
Connect your existing home theater AV receiver or Hi-Fi system to this compact preamp, then use your Wi-Fi® network to access all of your music from a simple app. Add other MusicCast speakers, sound bars or receivers for wireless multiroom audio playback. In addition to Wi-Fi, this preamp also...
usa.yamaha.com
The WXC-50 is a MusicCast pre-amp from Yamaha. If you are going with MusicCast, then this is the product specifically to use.
Also, I would look at the Sonos as a viable option. The Port is their current version of the Connect, and includes integrated volume control (from your phone/PC).
Introducing Port: the versatile streaming stereo upgrade from Sonos. Enjoy streaming music, podcasts, audiobooks, and internet radio on your existing stereo over WiFi with just one simple connection. Control your audio with Sonos app or Apple AirPlay 2, and easily expand your system to more rooms.
www.sonos.com
I'm sure there are is a long list of other possibilities as well.