Regarding speakers\Amp to improve the PSR9000. It so happens that the 9000 has a very good speaker system, possible due to them being built into wooden cabs. The YST_MS50 Satellites + Sub bass of the Pro & Tyros will not greatly improve on the speakers that are already built into the PSR9000. The Satellites are Harsh and the Bass Unit Booms.

Myself (9000Pro) for home I use my Hi-Fi System (as Dreamer suggested) but I have built a Bedroom Studio containing Large Studio Transmission Line Speakers. these are on Spiked Stands placed on concrete slabs. They produce very low clean Bass.

The 9000 is capable of producing some excellent sounds. The speakers supplied with the Tyros do not do full justice to that board either.

Graham UK