Yamaha stepped up their game with the PSR-E453 and successors. AWM2 tone generations is pretty much the same in all models. The number of tone generation channels, waveforms (samples) and digital effects vary depending upon generation.
Prior to that model, SWL01 (and variants) were widely used. The CPU and tone generators are integrated in one part, the SWL01. The SWL01 has 32 tone generation channels and minimal chorus/reverb effects.
Yamaha introduced the SWX03 starting with the PSR-E453. The SWX03 has 48 tone generation channels (i.e., polyphony) and ten DSP effects in addition to chorus/reverb.
I believe that Yamaha also made improvements in the waveforms beginning with the E453. Even the PSR-E363 claims "improved sampling." The E-series waveforms are still not up to the same level as the S-series.
Hope this helps. I can gab about this all day, but it might be a case of TMI for folks who just want to make a purchasing decision.
All the best -- pj