Is anybody using any such apps to remotely operate the AX53? I can only start and stop recording, nothing else. The problem is when I switch to "Ctrl with Smartphone" all settings default to "Auto" and the video becomes useless for my purpose. At least if it would let me retain my white balance and adjust the exposure the footage would be usable.

I can't help with that, but the AX53 annoyed me and I sent it back and got the AX100.
The remote software from Sony is very basic compared to Panasonic which allows way more manual remote control (WB,Focus etc) via the smart phone.