Are you saying that desires add in pleasures? Or that desires equate to pleasures? Or desires are additional to pleasures and pains?
There are some desires for adding in experience of sweetness and enjoyablenes, and there are some desires which are to stop the experience of pain. Eating chocolate cake is a desire which brings in extra stimulation beyond just the removal of hunger -- and if it was just for removal of hunger then we could eat bread instead of cake. If we eat too much cake we may start to feel overly full, and so we then stop eating cake to stop the discomfort. But there are other desires for additive pleasures besides just eating cake.
And some people may be more oriented (motivated) to stop pain rather than seek pleasure. For example a person who calls up a friend to talk because they feel lonely (and want to remove the pain of loneliness) vs a person who calls up a friend because they enjoy telling jokes and laughing together (desire for adding in fun).
Since the purpose of the inscription was evangelism, saying that we've excised and minimized pains is much more appealing to the average passersby than saying we've excised and minimized desires. Working with desires is a way that pain can be minimized, but that detail can come later.
lol -- this made me laugh, and yet there could be truth to it. But of course this brings up the whole "tranquility problem" -- which for me seems unresolvable. To be tranquil or not to be tranquil - perhaps we have to move beyond the "either/or" -- because sometimes we will take on pains if future pleasures will be greater.