Excellent reviews.
I still have a DGX-640 from back in 2010 (my cat uses it now as a bed). The grand piano sample (not CFX) was actually quite nice and natural when just testing out individual notes, however it is quite weak sounding when playing, and the built-in speakers are plenty loud. But sample technology on a 2010 budget instrument is forgivable. The worst thing about it is the keys have a very noisy echo, and when they keys are pressed hard there is a hideous creaking plastic sound from the chassis. The instrument weighs a lot and build quality seems good, so this is really unacceptable. We joke at home that these are all just special Yamaha “effects” they included in this model. My point here is that even though this is an instrument from 2010, I would certainly hesitate to buy an updated keyboard from the DGX line based on this experience.
Rich