I ordered the double bass unit from Musician's friend also.

Are you saying use both inputs because it makes the Yamaha stuff sound fuller, or do you mean everyuthing?

Also which presets are the best for the arrangers?

On the Bose forum, i was told to use ch1 for a direct mic and select the preset for that mic, use ch2 for the keyboard with the appriote preset then use ch3 for the ouput of my mixer.

Also how many players can you get into one of these things ( using a mixer of course ) until it becomes too much for the unit?