Problems sustaining pitches in Combo mode?

[mlung82]

Hello, this if my first time visiting this forum and forgive me if this has been answered elsewhere, but I don't have time to search extensively and need a solution fast.

I have a combo of 8 instruments prepared for a show I am playing. When I am playing these instruments, the keyboard will only allow a certain number of keys to sound simultaneously. For example, when playing a rapid harp arpeggio or scale effect the ringing of the lower pitches gets wiped out as I ascend. It's as if the keyboard does not accept more than 5 or so pitches to sound at the same time. Does this make sense? It is impeding my performance, and I am clueless as to how to fix it.

Thank you for any help