Awkward as several other passages are, I've always found that the biggest technical challenge is controlling the pianissimo trills right at the start. This is one of those occasions where knowing the piano you're playing on is essential. That very first whispered trill has to seize the listener's ear while only just over the threshold of audibility - if you adopt a low-risk approach and don't start with anything lower than an ordinary piano, there's no magic. Take it down too far and you lose notes, a disaster from which the rest of the performance is unlikely to recover.
It's the lower reiteration which is marked piu p - but the point is that in these six opening bars, from a cold start, you need to control the trill (and the following demisemiquaver figures) through the whole range of soft dynamics down to near-inaudible. The same six bars appearing in the middle of a piece would be far less challenging.
As I said, in my henle score the trills in the beggining are not so soft as you say. Also, in all recordings I heard they are played quite forte. Are you really talking about the first measures? If so, what made you think it's supposed to sound so soft?
It's the range required throughout the first six bars - look carefully at the markings throughout, including what happens after the piu p. These six bars are like the introductory bars of the Chopin 4th Ballade: they tell you that some sort of magic is about to be revealed, but what kind of magic remains a mystery until the piece proper starts. You can only really appreciate this properly in live performance: recordings, however good, inevitably mask these subtle dynamics. Michelangeli was electrifying here. Play them as a run-of-the-mill flourish, and they become pedestrian - all magic is lost.
Hi, I am not sure how beneficial this will be if you are looking for technical ways to practice it, but here is a master class that I was in with Paul Roberts... someone who has lived with debussy his whole life and recorded all of his piano music...
I am not kidding you, I actually watched that masterclass just over two weeks ago.Your playing is very deep and wonderful! That fact that you have only been playing piano for 3.5 years just makes it even more so impressive!What an honour to have you on the forums!