Using two plugins

i see a vst plugin that uses 2 plugins.

i mean first one for track, second one for mixer(empty track - just mix)

does anyone know how to work it;?


since several month ago, i am interested in multi track input.

so using DAW -REAPER, I use receive &send track to mixer track(empty).

i use 2 track first one for 1-2 channel, second one is 3-4

so attach my vst plugin to mixer track. and i get buffer data separated in channel(1,2, 3, 4)

in processBlock function.


however the amazing vst plugin that i said before are using just 1-2 channel (track, mixer both)

difference is just using 2 plugins. So is method exist  i don't know for multi channel input

or are they using IPC for buffer data moving via plugin.


i don't know where i research or study. 

links are here.