Advanced tone editing is possible via the Tone Tyrant software, released by mrmr9494 here on the forums. The AiX sound engine has a complex envelope with multiple Attack and Release parameters that can approximate the decay and sustain functions on a synth with a normal four stage envelope. Casio built all this functionality into the .TON files themselves, but did not make the full set of parameters available via incoming MIDI CC or the built-in tone editor menu. I believe Tone Tyrant can also help with DSP block editing, but I haven't looked into that too deeply.
Basically, you would do the preliminary tone edits through the built-in tone editor, and then when you reach the part of the sound design process where you need to tweak the hidden parameters, export the "rough draft" .TON to your computer for fine detailing via Tone Tyrant. Then you save the modified .TON and send it back to the CT-X for testing. Fortunately you can import and export files directly to the keyboard from within the program so there's not too much waiting to see the effect of your edits -- "realtime" software editing with instant updates has yet to be figured out.
You can find the topic for Tone Tyrant here.
Not too sure on the specifics of the 4 band EQ. You might try emailing Casio support to see if they can clarify, the information is not published anywhere as far as I'm aware.
Chandler Holloway's post in Tips & Tricks about, setting, programming, playing, and controlling, the Casio CT-X5000 was marked as the answer