Updated Audio modes demystified (markdown)

Audio-modes-demystified.md

@@ -239,6 +239,10 @@ Allows you to upsample / downsample exclusive mode streams. This can be useful i
 
 Allows you to modify the buffer size. This can be used if the buffer size requested by the game engine is too low (e.g., SDVX requests 3 ms) and causing static noise in your speakers. You should start with 10 (10 milliseconds) and slowly increase it; higher values are safer, but will add more latency.
 
+## ASIO 7.1 to Stereo "Downmix" (-asiodownmix)
+
+This performs a downmix from 7.1 to 2 channel by extracting audio from specified channels and routing them to the front speakers (e.g., rear channels to front channels). It doesn't do any *mixing*, just swapping of channel destinations (just a `memcpy`), but can be used if the game is outputting audio to the wrong channel.
+
 # Other audio hooks and hacks
 
 [REAL](https://github.com/miniant-git/REAL) was used in the past to minimize DSound and shared mode WASAPI latency, but it is longer needed as the feature has been integrated into spice2x as of 2023-11-23 (see `Audio latency reduction for DSound and Shared Mode WASAPI` section above).