The game is both designed to only allow a single captive to reward you and not designed in a way that enables multiple captives to reward you. There was a mod by ANGERaw that that addressed this, but it has been outdated by a few versions and will probably not work with v1.0d.
There are several stats that govern how slaves react to "mana plundering": Consent(from Request Intimacy), lewdness, lust, and loyalty(only a factor if they have not given consent). Participating requires moderately high lust and reduces lust a fair amount, so "Meh" is indeed the typical reaction. The only ways around that is the Living Armor or Sex-crazed trait.