You have an embarrassment of riches to choose from using 2 H90s for this. Let’s assume one to generate harmonics, and the other dedicated to standard wild-card effects.
At the start, you might consider two copies of any algorithm suggestion here in Parallel. In that way, you can ‘build’ a larger version of it with complementary (offset) parameters in each.
My first thought for adding ‘harmonics’ was pitch-shifting. The newest SIFT algos (Polyphony, PolyFlex, Prism Shift) may be your cleanest option, but with recorders as input, I wouldn’t overlook any in the Pitch family.
Distortion came to mind, and it doesn’t need to be maxed out. In fact, something like PitchFuzz might be ideal, blending in added harmonics with a bit of hair on them, and still have delays as a sweetener. Sculpt can split the spectrum across channels, and yet Aggravate might give you a more immediate experience. A blend of harmonic, distortion, and synthesis.
Which all brings me to my actual 1st thought @Synergist: the Synths. You won’t have any more problems blending into a band context with PolySynth. With true monophonic input, I wouldn’t ignore HotSawz. Each one has its own unique strengths. And you’ll get the ability to manipulate timbre & harmonics with a host of other options.
Now consider two in Parallel (as above), or a combination example in Series [Polyphony into PolySynth, etc.] One H90, with the other still available for the usual downstream processing.
Let us know how you make out. This is an unusual & interesting use case.
