the only true point of view, is full of hope that he, the hub of the cosmos with his hair blown sideways,
We get more hyperbole and exaggeration in these lines. Here the speaker refers to himself as "the only true point of view" and the "hub of the cosmos."
The speaker knows that his isn't the only "true" point of view, and that he isn't the hub of the cosmos. We mean, everyone walking past him thinks the same thing about themselves. But the music is making the speaker feel as if he is the only "true" point of view and the "hub of the cosmos."
It's also interesting that the speaker is referring to himself in the third person here: "he," not "I." It's as if he's looking at himself from the outside. This is also a way of putting himself at the "center of the universe"—it's as if someone else is looking at him and talking about him.
We also get a detail about the speaker's looks. His hair is "blown sideways." This gives us a sense of a nice spring breeze. Who wouldn't be happy listening to jazz while a spring breeze blows their hair sideways?
There's a lot of familiar alliteration in the lines, "is full of hope that he, the hub of the cosmos/ with his hair blown sideways" with repetition of those H words.
will eventually make it all the way downtown.
The last line of the poem is kind of like a joke. The speaker's set up all of this expectation in the previous lines, telling us that he's the "hub of the universe" and the "only true point of view." We expect big things from this guy. How could we not if he's the hub of the universe?
And yet, all the speaker hopes, as the "hub of the universe," is that he will eventually "make it all the way downtown." The speaker pokes fun at himself here. He puffs himself up only to tell us that his only ambition is to walk downtown.
Even though getting downtown may not seem like a big deal, the speaker is making an important point here. This guy doesn't have any grand plans or ambitions. What this suggests is that the speaker is living in the present. He isn't worrying about anything except getting downtown. And it's the music that's allowing him to do that. So the jazz that the speaker listens to transforms him in two ways. On the one hand, it makes him feel super-powerful and important. On the other hand, it allows him to focus on the present, to forget about big worries or plans, and to just enjoy the moment of… walking downtown.