Equalizer APO might be what you're looking for.
After downloading and installing (and restarting Windows), however, it will take a bit of configuration to achieve what you need:
- On first start, it will ask you to configure the output devices. Select your main output device, usually
Speakers - VIA HD Audio
or Speakers - Realtek HD Audio
or something like that.
- In the Equalizer APO Configuration Editor, click the red minus icons next to each of the active filter items to remove them all.
- Click the green plus icon, select
Basic filters
, Copy (Copy between channels)
- Drag the red
L
over to the green R
below it, which will create an arrow pointing diagonally from one to the other. Repeat the same for the other side, dragging the red R
over the green L
.
If the power icon for that configuration is white, it means your stereo has been swapped. If it's black, it's off. Run some tests to verify this.
This is a simplified, GUI version of the manual configuration task, originally suggested at Seven Forums.