So as I stated "easiest" is using the socket inside:
There are 2 black plastic connectors, in this picture the "dc shorting plug" is in place in the further of the 2 connectors.
Is this what you have?
If you don't use the socket (the easiest as you requested), then virtually any other "DC" sound card is equal effort, and you will have to hard wire to the board in a few places.
All the other DC sound boards are thus pretty much equal in "difficulty"...
Now, if you will reply to the questions about ease vs. cost... perhaps the most economical way would be a MyLocoSound board, significantly cheaper and configurable..
an excellent dealer by the way..