I spent about two hours today trying different setttings on my BK9 for a proposed gig. Its a two hour opener with a guitar player. Opening for a band at the Bluffton Beer and Bar'Bque sunset party. I hit the track mute button on the BK9 and that shuts off all the Arranger sounds except Bass/Drums. Then expierimentsed with full keyboard Piano. Reading both hands the arranger not only followed me but came up with some intricate chord interpretations. #9s, b11ths, chord/bass, etc. So the answer is yes our Arrangers can do this stuff but we have to modify our playing from splitting the keyboard and holding simple chords with out LH.
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Bill in SC --- Roland BK9 (2) Roland BK7M, Roland PK5 Pedals, Roland FP90, Roland CM30 (2), JBL Eon Ones (2) JBL 610 Monitor, Behringer Sub, EV mics, Apple iPad (2) Behringer DJ mixer