I just checked this on my Audya 4 and found the same problem.
Using a Midi keyboard to control the Audya4 and selecting Master 1 in the Midi settings page there is no Bass heard when I have the Manual bass selected.

Another problem with my Audya 4 is it always loads the Accord 1 Midi setting no matter how many times I use the SAVE Midi setup or Custom Startup.... I have to go into Midi settings to change it to Master1 every time I switch the Module on.