Let's step through this one more time then.
Goldwave can open AC3 when an AC3 codec is on your system. It does not natively know what an AC3 is, so you are correct to go to "All file types" to find your AC3 audio.
If you've not clicked on anything else, a small pop-up box will open on top of Goldwave, and will show a slow and steady progress bar "Processing Audio Decompression"
that is opening and decompressing the audio into a temp file for the editor.
In general, you don't have to select the audio, but you can if you want. Simply click anywhere on the audio timeline, then go to EDIT > SELECT ALL, and your full audio timeline is selected.
Finally, go to TIME WARP and enter in the exact time differential specified by VirtualDub
, and it will also spent a great deal of time "Processing Time Warp", again in a small pop-up window.
After that is done, save as a new WAV file.