The Yamaha PSR-SX700 is a 76-key workstation that features advanced content creation capabilities. The Yamaha DGX-660 is an 88-key digital piano that offers an authentic grand piano experience. Both keyboard workstations are equipped with powerful processors and a variety of high-quality voices and styles. However, the PSR-SX700 has more polyphony (128 vs 64) and comes with over 1700 Voices and 550 Styles. It also has an external storage option via a USB flash drive, while the DGX-660 does not. Finally, the PSR-SX700 has a larger color LCD display (7" vs 6.3"). If you're looking for a keyboard workstation with more features and voices, the PSR-SX700 is the better option. If you're primarily interested in an authentic grand piano experience, then the DGX-660 would be a better choice.