Hi, and welcome!
The main difference is that the DGX-670 is primarily a digital piano, whereas the PSR-SX700 is an arranger workstation. This makes them completely different instruments.
The DGX has a piano-like keyboard, with 88 weighted keys (like a grand piano). This key are a lot harder than typical keyboard keys, and feels more like a piano mechanism. But, on the other hand, it has a much smaller selection of instruments, styles ands DSPs, and no MultiPads. But the main piano sound is much better than on the PSR.
In my opinion, your main decision criteria should be your past experience: if you come from a piano background, the DGX might be a better choice. If you come from a keyboard/organ background, I would go with the PSR. The heavy piano-like keys take some time to get accustomed to, if you come from a different background. If you can try them, this might give you more insight into the differences.
Regards!