Mike,
I would consider the PSR1K or the PSR2100 over the PSR550 for your purpose. The PSR550 has a very complicated sequencer to use compared to the other ones. Because it must record direct to disk and the others have internal sequencers, I would rather recommend these two for a guitar players use.
Most of my guitar player customers like to be able to lay down accompanament tracks and then play guitar or sing over them. With the two I'm recommending, the record process is much easier.
George Kaye
Kaye's music Scene
Reseda, California