Yes, when the output mode is auto (which is the default setting) the H90 will automatically sum to mono, or mult to stereo when necessary to handle the mono inserts correctly. If the outputs of your H90 are connected in stereo, and you put and algorithm as the last block in your routing chain, that effect will be in stereo. On the other hand, if you have a mono insert as the last block in your chain, the H90 will output a dual mono signal. More information about the routing behavior can be found here: https://cdn.eventideaudio.com/manuals/h90/1.8.6/content/system-menu/io.html