But there must be one more place that needs the same type of fix yet for GANG audio mode.  This is currently working if you drag an audio plugin to a 2-channel audio track - that is, when you get back to regular mode you can see that the plugin is on both audio tracks.  But when you have In/Out pointers and use the "attach effect" method instead, it only shows on the initial track.

i tried to add two more lines into mwindowedit.C

and for me I can select in/out points for two gang modes where sound tracks collapsed on timeline (with 6ch divx) and then use audio > attach effect for inserting effect and it propagates correctly

Not sure why but this patch did not work for me.  When I drag effect from Resources in Gang Channels mode both tracks of 2-track audio get the plugin.  BUT when I attach effect only the 1 channel gets the plugin.  This is with just the 3 first patches in (not the 0004-Attempt-at...which I will comment on later).  Andrea, did this work for you?