It shouldn't be a problem, I agree. It might actually help, to sculpt the desvenlafaxine to a more desirable end benefit, but you never know until you experiment a little. SNRIs like this (with mixed SSRI activity) are shown to increases cortical GABA in depressed patients. Progressive pain disinhibition of central origin may product a noticeable antinociceptive effect with such a combo also, and that can certainly be desirable in some conditions. You may be able to reduce doses of one or both if adverse or excess synergism occurs, and I'd bet your doc would know how to calculate that if you're own trial and error doesn't establish it. God bless you my friend, and I hope you find the solution you seek!