Winging this, off the top of my head: I think you’d need the Looper as one Preset instance, and the ‘completely different sound’ as the other Preset. Insert Mode Program. Looper first, in Series, if you want the loop to be processed by the ‘other sound’, too. Other sound first, in Series, if you want the loop to remain unprocessed [Loop Mix @ 50%].
Probably the cleanest way would be the Looper and ‘other sound’ in Parallel, each 100% wet, then fold in your input at the Program level. I’ve posted some H9 / Timefactor threads on storing one-shot loops, so you can adapt that to something similar in the H90. [Playback mode switched away from one-shot; to one of the looping modes].
Obviously, this will be a two-part process: Record the loop, start playing it back, then play over / alongside the loop with the ‘completely different sound’. That is, unless I am misunderstanding your question, and the loop is already stored on a device external to the H90.
