I think that the idea that Boulez composes "pretty sounds" would be taken as an insult by him.
As he says "All these years, I’ve been trying to convince people that music is not there to please them; it’s there to disturb them.’
You're right, "pretty sounds" is the wrong way to put it. But Boulez would not have been insulted if his listeners took pleasure from his music and deemed parts beautiful. I don't only listen to Boulez for the beauty, his music is richer than that.
Here he talks about conducting, but the same could apply to his music in general:
"The sensual pleasure afforded by the work?"
P.B. "An accurate performance of the work includes that. It also involves translating it into sound, and when that's done properly, it satisfies you intellectually and physically. In the end, that's all that counts...
"And that's pleasure?"
P.B. "Oh, it's far more than pleasure. If that's the vocabulary you want to use, it would be better to say 'joy' rather than 'pleasure'."
Conversations with Boulez: Thoughts on Conducting
I was being confusing and superficial with the concepts I was using. Was just seeking recommendations on contemporary composers with the "sonorous qualities" that (poco) Sforzando articulated. However, I do agree that might be completely idiosyncratic, like amw said. Maybe people find the music of Xenakis, for example, just as beautiful as the music of Boulez. Despite not being clear, I have received plenty of great recommendations here, thanks again.