Here, as kāmā is plural, it clearly refers to the external sense stimuli. So yes, I agree with Sylvester; in this case, Ven Thanissaro’s translation is incorrect.
However I prefer to avoid the use of the word “object” when talking about early Buddhism. There is no term in the description of sense experience that corresponds with the idea of “object”, which is a translation of the commentarial term ārammaṇa. In the EBTs, sense experience only happens in relationship, hence there is no room for an “object” that exists independently.
It’s true that “sensual pleasures” is ambiguous here. Perhaps “sense stimuli” would be better. @Brahmali, what do you think of this?