Of course, if you want to take advantage of 'open' chord voicings on an arranger, you'll generally have to use your 'Piano Mode' or whatever your arranger calls it, where it looks at the entire keyboard as you play pianistically.

Roland have a nice feature of Pianostyle Mode, where you HAVE to play at least three notes to get a chord change, so you play your big 'open chord', and then solo one note at a time over it, and the chord won't change. Perfect for new age things.... (you can also try programming a foot-switch to turn Chord Recognition 'off' while you solo, and back on for the next 'open' chord - new age tends to have very slow chord changes!)