I don't know about Casio keyboards, but I would ask you these questions.
Does the Casio have a 16 track sequencer with a 165,000 note capacity? The Yamaha 540 does.
Does the Casio allow you to make your own user styles(patterns)? The Yamaha 540 does.
Does the Casio have XG, not just GM sounds?The Yamaha 540 does.
Does the Casio have Registration memories to store your favorite settings? The Yamaha has 128 memory locations.
Does the Casio offer a multi effect DSP effects processor besides Reverb and Chorus for using effects like Rotary Speaker, Guitar Distortion, Wah effects, etc.? The Yamaha 540 does.
I really don't know if the Casio's offer these features, but I don't think so from what I've seen and read. Check these features out, because this is why I sell so many 540's in my store. The Yamaha offers so much bang for the buck, and one more thing I forgot to mention, is when you are playing midi files in the disk drive, the Yamaha has a revoice and volume mode that allows you to quickly by just pushing one button, change the sounds and volumes for all 16 tracks of the midi file, and if you like these changes, there is a mode for saving them on the disk. I've always thought that the more recent models of Casio sound much better than they did before, but I find their feature list to be somewhat limited.
George Kaye
Kaye's Music Scene
Reseda, California