I've had a bit more of a play with the cable and app and now I think I see how it works. Sorry for telling most of you how to 'suck eggs' here, but I'm still trying to figure out how this thing works.
In it's original state, before connecting it to the audeze app, the eq settings that the cable uses for playback when connected to the iPhone are native to the cable and are set for the i3/i4 (if you have the i3/i4 cable, of course). When connected through the Audeze hq app this allows you to change the native i3/i4 setting in the cable using the 10 band graphic equaliser sliders. I didn't realise, but when you create presets in the app the basis of the presets is the native i3/i4 setting (ie 0 dB on all the sliders on 'preset 1' is not a flat output through the cable, but rather no change to the native i3/i4 setting). So when you adjust the eq settings you are adding to or subtracting from the native i3/i4 setting - again, not how I thought it worked. My question was, how do I select between the different eq presets that I have created - I assumed that I could press a combination of buttons on the cable to get either the native i3/i4 setting or either of the two presets I've created in the app - not true as far as I can see. From what I can see, the EQ setting used for playback by the cable is either of the 2 presets, and it uses the last one you had selected on the Audeze hq app.
Obviously, the cable and the app need to work together for this to be useful. From my brief use, it looks like the Audeze hq app and the cable are working together as they should, in my case. When I create a preset in the Audeze hq app the cable appears to be saving that setting. To test, I created a bizarre eq in the app (something that I could easily pick from the native i3/i4 setting), then closed the app on the phone, disconnected the cable and plugged the cable back in. When I listed to a song it was obvious that the new (bizarre) setting was being used (and obviously, saved in the cable). Also, when I re-started the Audeze hq app and went into the EQ area in the app, the bizarre eq setting that I had created earlier was still showing on the eq sliders.