I also think in relating the issue of discrete sensations of pleasure to the issue of "pleasure in total" we will need to take note of something specific: I don't think that Cicero would leave himself open to the charge that he was intentionally misrepresenting epicurus by having Torquatus say something that Epicurus did not believe, I DO think Cicero intentionally would not provide the whole explanation. The prime example I would point to on that is near the end of the Torquatus exchange in on Ends Book two, where Cicero says that Epicurus held that the host pouring wine was in the same state of pleasure as the guest drinking wine. As I understand the text, part of the hypothetical is that neither of them are in any state of pain. However they clearly are engaged in very different activities.
If Cicero had allowed Torquatus to explain this he would likely have given us exactly the explanation we are looking for - how two people experiencing no pain are nevertheless experiencing very different type of pleasure.
But rather than allowing Torquatus to explain, Cicero has Torquatus cut off the conversation at this critical point to accuse Cicero of quibbling.
I think this points to the direction we are going - that OBVIOUSLY Epicurus understood that being without pain is not a specific type of pleasure. Instead, for a description of what a particular person is experiencing, you have to look to the actual activities of the actual person at that particular time and place . Saying he is "without pain" says NOTHING about the particular pleasures in that person's mix of experiences except that he is at the "limit" and can experience only variations in pleasure. He can experience new types of pleasure to change his mix, but he cannot experience a higher "quantity" of pleasure. Of course identifying the limit is highly important in responding to Plato and Seneca, but most normal people are expecting a discussion of a particular experience of a particular pleasure, and when they see this instead they are left confused. That confusion has to be dealt with.
I will likely include this in a future revision but it is exchanges like this which tie discussion of discrete pleasures immediately to discussion of the limit of pleasure that i think make it unavoidable that they be discussed together.