You use a combination. Pg 26 of RMSS says: "The conditions which interfere with casting spells from each of the three realm (see Sections 26.0)... When casting one of the spells from his base lists, he suffers the interference from both realms" If you look at the * mark on the table, it's note says "With each condition, use the worst (to the caster) mod. applicable during any preparation round or casting round". So your sorcerer with no free hands would use the essence -30 and no voice would use the channeling -10.