Before I go any further I should point out that I am not a techy. This is a solution that works for me. I am sure that others can improve on this. (I also apologise if I havent used the correct terminology for windows, dialog boxes etc in my description).

I have XP64 so it I dont think that it is a straight forward option to control Omnisphere from my Ipad using WiFi MIDI. I have had some success with Line6 Midi Mobilizer but it is not Wifi and not all apps support it. After a bit of frustrating research I came up with this solution

1. Get a copy of DSWifiMIDI server for Windows from here:
2. Get a copy of LoopBe1 Virtual Midi Driver from here:
3. Run LoopBe1 exe file. This opens a small window on your desktop. Leave it running
4. Run DSWifiMIDI This opens another window. Choose LoopBe Internal MIDI as the input and output ports. Leave it running
5. Open Ableton Live and in Options/Preferences/MidiSync , you should see LoopBe as Input and Output options in the MidiPorts box. Turn both Track and Remote on for both.
6. Open your Omnisphere in Ableton
7. On your IPad open the App that you want to control Omnisphere. I use ThumbJam or StepPolyArp. Look in the settings of the app to turn Wireless Midi on
You should now be able to play the synth from the IPad

If you have no response first check that Ableton is receiving a MIDI input by looking at the Midi Track Indicator box (the small yellow flashing box top right).
You can check that you have a midi signal by trying the free iXY controller app on your Ipad before you spend money on any apps. Although it doesnt make a sound you should get a response from the Ableton Midi Track Indicator

Hope this is of help to someone. Sorry that I cant help if you have any probs with this. It just works for me