This is an attempt at making a better Sonos controller for iOS. It's pretty hacked together right now -- I'll try to articulate needs later so others can contribute. The following (sparse) instructions below should get it working with your system.
Easiest way to do this is to checkout: https://github.com/rahims/SoCo and use the command line example. Run: python sonoshell.py all list_ips to find all the IPs. Then run python sonoshell.py YOUR_SPEAKERS_IP_ADDRESS info to determine the uid for each speaker.
Now open the file PLNowPlayingViewController.m and replace lines 79-82 with your speaker information. Compile and you should be able to control the volume of your speakers.
