Squeak,
The PSR550 is double the price of an EM20, so Roland did a really good job. Of course the PSR550 has all kinds of features like disk drive, importing custom styles, all kinds of handy buttons. The styles are better as well. On the Harmony-Central synth forum one poster said the Yamaha PSR piano sounded like thumb tacks falling on rusted guitar strings. That sounds about right. The piano sounds more like a guitar then a piano.