What we think:

The PSRS550 has a fantastic production range using a 16-track sequencer and Style Creator. It also offers improved performance through increased polyphony and voice variations. However, it's real triumph is quite simply the quality of sound, which is exceptionally clear and powerful whilst still maintained in a small portable package. 

• 61 full size touch sensitive keys.
• 769 Amazingly realistic AWM / XG / XM Voices -digitally recorded instruments using Yamaha's AWM technology for superior sound!
• 64 note Polyphony..
• Full dot LCD Display - provides 'at a glance' control over the full range of performance settings.
• Score and Lyric Display
• Numerous types of  Reverb, Chorus & DSP Effects and EQ's- adds an extra dimension to any performance.
• Great functions - including Dual Voice layer & Orchestration- place an instrument in each of the Main, Dual and Left sections. Panel Sustain, One touch setting and Poly/Mono, Octave and tuning + many more!
• 4 One Touch Settings for each style, with OTS Link - manually select a suitable voice for every part of the accompaniment style, or let the keyboard do it automatically with OTS Link. 
• Music Database - you want to play music in your favourite style, but you're not sure how to select the best voice and style for the type of music you want to play-simply select the appropriate style from the Music Database. The panel settings will automatically be adjusted for the ideal combination of sounds and style! Choose from an onboard list of 600+ Titles, and the keyboard sets itself up with an appropriate style and registration.
• Auto Harmony - adds chordal harmony based on a single-note melody.
• USB to DEVICE- allows USB memory such as thumb drives to be used for data storage.
• USB MIDI connection -  MIDI connectivity is possible via the USB to Host Port
• Flash Memory (Internal) 800KB
• Sustain pedal & headphone socket. (Headphones and Sustain Pedal can be purchased separately).
• 16-track sequencer, 5 songs and 16 channels.
• In built metronome.
• 2 x 12cm Speakers with 12 Watt Amplifiers.
• Includes Yamaha Power Supply & Music Rest.