Please see my other messages on this topic.
QSI made two types of decoders one for the Bachmann locomotives with all the pins connected and one for the Aristo locomotives with none of the extra functions connected. They did this because they found that there were Aristocraft locootives that had random power connections to J2 and a smoke function that they did not support.
Revolution Train Engineer decoders have sockets for the extra function but you must manually connect these to the solder pads on the Bachmann locomotives for these functions to be controllable.
I have no direct experience with the more recient Digitrax decoders but expect the same thing.
While there have been several truly plug and play DCC sound decoders for Bachmann locomotives, currently there are only two in the market currently. One by Zimo and one by Phoenix. I have both.
I do have concerns that the 4 motor Dash 9 has the potential for more current draw that the Phoenix is designed for.
The main reason for the current lack of true PnP decoders is that since 2007 Bachmann only released one locomotive every few years with the socket and Aristocraft is no longer around. Thus the market was small.
Lately this has changed due to the release of several new locomotives with the socket. I fully expect more choice in the market in the comming year. Until then, the best option for the Dash-9 right now other then the Zimo PnP decoder is to use any sound decoder that has both a + and - connection and connect it the the plug in board with wires attached. This board is supplied with each locomotive.
One other comment. The switches on the Dash-9 work as follows. In the On position the device in the socket controls the function. When the switch is Off the function is off no mater what is in the socket.
You can change this by making connections to the solder pad between the desired function and ground If you make this connection the corresponding switch can be used to turn on and off the function no mater what is in the socket.
Hope that helps