Like Lepou, Ignite, ecc.
My question is : I know how to use them as ''posteffects'' on a track previously recorded clean. But I've no clue how to use them in realtime like I do with guitarrig, amplitube and other standalone ampsims.

Btw...I'm using Reaper as my DAW.
Click the speaker button by the Arm button on the track to activate monitoring; this will let you hear the track with any effects on it.