They are good, but I have no idea whether they are better. MX is older than PSR-SX, so I would think that PSR-SX might benefit from newer technology, but MX is a synth so its controls are designed to achieve a different goal than the controls on an arranger keyboard-- live manipulation of sounds as opposed to live manipulation of accompaniments. I should think they'd complement each other nicely on that account, although MX synths have an old, awkward-to-use interface-- meaning its menu system and its tiny screen display-- so you would want to grab some software for setting it up and editing its sounds.