The EX5 is one of the most powerful synthesizers Yamaha has ever released. In addition to its built-in AWM2 ROM and sampler capability, it also has virtual analog, virtual acoustic, and FDSP (Formulated Digital Signal Processing) synthesis engines.
Any samples loaded will be forgotten when the unit is switched off. An EXFLM2 flash board that adds 16MB of non-volatile sample memory can be installed to make the keyboard remember samples across power cycles. Sector101 makes an aftermarket version.
It has "Sondius-XG" printed on the right side of the control panel. That refers to the virtual acoustic technology that Yamaha developed jointly with Stanford University.
The Yamaha EX7 is a less-powerful 61-key version of the EX5. It is also available in rackmount form as the EX5R