CYP2D6 inducers will, as you said, encourage the conversion of DXM to DXO. DXO is the actual compound responsible for dissociative effects, DXM itself is effectively a SNRI and sigma agonist.
I don't know if I would call one "psychedelic" and the other "dissociative". I would say "pure" DXM is a very stimulating high with mild motor impairment. DXO and conditions that encourage the formation of DXO give the powerful, almost amnesic dissociative, spacy, "calm" effects.
Also, not many people can source quinidine or dexamethasone ... I know quinidine is an anti arryhtmic agent, so it could fuck with your heart rhythm if you mess with the dosage. And dexamethasone is a corticosteroid: it's not a drug you should take systematically just to potentiate cough syrup; the list of side effects is about a mile long.