There are a number of incremental differences between them, with the A-S2000 having upgraded parts where is matters. IMO that's what makes the A-S2000 better than the A-S1000.
The A-S2000 is a fully balanced design.
The A-S2000 has a better phono stage (the phono amplifier uses discrete components).
I think there's plenty of love (appreciation) for Yamaha on AK.