I think the FLD6 has just a bit more sparkle, almost like the Foldiplier has a subtle LPF on it. On the scope it looks like the folds on Fold-6 were closer to Vpp too, while the Foldiplier generally let the folds sit more like 1/2 to 3/4 of Vpp. That feeback mode is gnarly, as a Fold-6 owner, I'm a bit envious.
Just make a feedback loop with your Fold 6. Mult the output and add it to the mixer feeding your Fold 6. Also try inverting the signal before feeding it back into the mixer for a different sound.
