The loader will protect you from using the wrong file. The first DCS files where for the PS-2 5 boards. This is the one piece board that uses the 8.4V battery. Only PS-2 5V sound files can go into a PS-2 5V board.
When MTH revised the board to the PS-2 3V board. A two piece board that uses a 2.4V AA like battery, the processor and memory are different so the file type is also different. Any 3V file can go into a PS-2 3V board.
The upgrade term is used to identify a file that was posted to support the Upgrade kit so it is a PS-2 3V sound file. PS-1 engines that did not have sound files will have upgrade sound files.
Since the PS-2 3V is a replacement board for the PS-2 5V they needed to upgrade the sound file for the replacement board. So a PS-2 5V engine will may have two sound files posted. One is the original 5V file. The second is the Upgrade sound file. This is the original 5V file reformatted to a 3V format.
Newer 3V sound files have date codes at the end of the file name. Any PS-2 3V file can be loaded into a 3V board with one caveat. Early PS-2 3V only had 1Meg of memory. Some later 3V sound files are larger than 1Meg. They won't fit. All the latest PS-2 3V boards come with 2Meg memory and can load any 3V sound file.
If you liked the sounds of your original 5V board than load the "Upgrade File" listed under your engine. Otherwise do a search under "Service" and "Files and documents" and load a newer 3V file. G
