When I connect my Privia PX-130 to my computer (and Logic) it works perfectly but if I connect the audio out (via line out) at the same time, the audio sounds dreadful, even if I'm not going through the computer. The problem goes away of I disconnect the USB, but of course this does not help me. USB cable is new btw.

http://www.circuit-encyclopedia.com/listinfo-67-111.html
Download Service Manual for PX-410R as PX-410R is the same model as PX-575r.

Casio don't supply PX330 drivers for IPAD.
Get a Windows 8.1 tablet or connect PX330 to a desktop PC and use IPAD to Remote control that PC.

You can download the service manual for free from manualslib.com

Try this
1. Turn off the digital piano
2. While holding down both the (TONE) and (FUNCTION) buttons, press the (POWER) button

Turn the Keyboard off the press and while holding down the [TONE] AND [FUNCTION] buttons power on the keyboard. Wait until all reset is done.

Make sure you follow the steps of the procedure below exactly. Connecting incorrectly can make data
send and receive impossible.
1.
Turn off the digital piano and then start up
your computer.
• Do not start up the music software on your computer
yet

3.
Turn on the digital piano.
• If this is the first time yo
u are connecting the digital
piano to your computer, the driver software required
to send and receive data will be installed on your
computer automatically.
4.
Start up your computer's music software.
5.
Configure the music software settings to
select one of the following as the MIDI device.
CASIO USB-MIDI

Check the midi channel. It needs to sync to FL Studio. Channel settings you'll need to look up in the privia manual...can be laborious - but worth it in the end :)

Refer to page E22 in your user manual. Please note that the default pitch is crystal controlled and quite accurate, but if you need to detune it you can do so as well as changing the temperment.

If I were to venture an educated guess I would vote for failing filter caps in the power supply.

The power is likely collapsing under load of the speakers but headphones take much less drive.

If this has an external wall-wart power supply, you might try a new one IF the output is found to be under the rated voltage.

Internal power supply components are beyond those individuals that are not adept at electronics.

WHich driver do you download for the midi? please, I dont have any idea. can you share a link where I can install or download the driver?