I think the sound quality you can achieve on the BK-9 for music outside of the typical arranger genres, here H�ndel baroque music and classical piano music (Brahms here), is really excellent. The BK-9 SN-A pianos are on the level of good digital pianos, together with a really good keybed, and if you pick the right strings sound, there is one identical to the SRX 04 expansion, it is exceptional too.
Add a small SonicCell or XV 2020 module with two SRX boards to it, and you have a truly massive high-quality sound selection.