The lack of 'lushness' on each of the sounds is due to each of the programs in the program mode using a unique, customized effects pair. When you go into Multi mode, all 16 channels share the same 2 effects processors. There is no way around this. The send 8/8 you are talking about turns up the 'send' level (the input level) of each part into the effects pair, which are doing chorus and reverb.

Each sound can have a send level for the first and second effect processor (send C and D) between 0 and 9.

Steve Martin
Ward Music Ltd.