Owner's Manual: https://www.roland.com/us/support/manual_archive/
Channel 1 - Note To Arranger. This is the Channel that is used to trigger the arranger from an external device like a digital piano or the PK-5 Foot Controller.
Channel 2 - Manual Bass. Manual bass is used for walking bass lines on the left side of the keyboard split. It is generally set an octave lower than the lower part, and on the GS compatible intelligent arrangers, this part is monophonic. It is also intelligent in that it plays the root of your left hand chord , even it if they are inverted
Channel 3 - Lower Part. This part is designed to be the left side of a keyboard split. On high end E series, it can be layered with the Manual Bass and it can also be layered with the accompaniment parts.
Channel 4 - Upper Part. The part is designed to be the right side of a keyboard split and the melody part when playing the arranger. On E series that do not have an Upper 2 part, the Upper part is also used for Melody Intelligence. Melody intelligence is a harmonization of the melody line based on the chords that are being played in the left hand.
Channel 5 - Accompaniment 1. This part is used when the arranger is in Advanced accompaniment mode. It plays the added spice parts like brass stabs or string lines.
Channel 6 - Accompaniment 2. This part is also used when the arranger is in Advanced mode. It is the main accompaniment part such as piano or rhythm guitar.
Channel 7 - Accompaniment 3. This part plays back when the arranger is in Basic accompaniment mode, and it is the only accompany part that plays in Basic mode.
Channel 8 - Accompaniment Bass. This part is dedicated to the accompaniment bass.
Channel 9 - RX Only. This is a blank part that is not used for anything in the E series. It is designed to give you an extra part for MIDI sequencing applications.
Channel 10 - Drums. This is the channel for both manual and accompaniment drums.
Channel 11 - Sound FX. This is the channel used for the FX that you assign to buttons on your keyboard.
Channel 12 - Not used by Intelligent Arrangers. This is not used for anything on any E series.
Channel 13 - Upper Part 2
Channel 14 - Not used by Intelligent Arrangers. This is not used for anything on any E series.
Channel 15 - Not used by Intelligent Arrangers. This is not used for anything on any E series.
Channel 16 - Control Channel. This is the channel that is used to receive MIDI program change messages to modify music styles and do real-time control of the arranger with features like Fill to orig, fill to Variation, Start/Stop, Basic/Advanced Break, Mute etc.