ambling along 44th Street with Sonny Rollins for company (3-4)
The speaker talks about Rollins keeping him "company" on his walk in these lines. He makes it sound as though Rollins is actually walking right there beside him, chatting to him. Of course the speaker is just listening to Rollins' music, but the way he talks about listening to this music (with Rollins keeping him "company") makes it sound as though they're old buddies and friends.
[…] my gratitude to Tommy Potter for taking the time to join us on this breezy afternoon (15-17)
By saying that the bass player is "joining" him and Rollins on his walk, the speaker begins to give us a sense of a music community that he's a part of. Listening to Potter on his earphones makes the speaker feel as though Potter is a friend "taking the time" to join him on his walk.
and to the esteemed Arthur Taylor who is somehow managing to navigate this crowd with his cumbersome drums. (18-20)
Again, here the speaker gives us a picture of the drummer Arthur Taylor "navigating" the crowd that the speaker is walking through with his "cumbersome drums." By evoking this image of Taylor walking along with him, the speaker gives us a sense of the friendship or camaraderie he feels with these musicians.
And I bow deeply to Thelonious Monk for figuring out a way to motorize – or whatever – his huge piano so he could be with us today. (21-24)
Monk is the fifth musician who joins the speaker's jazz crew. By depicting Monk walking along with him, the speaker suggests that Monk is his friend.
because the five of us, instruments and all, are about to angle over to the south side of the street and then, in our own tightly knit way, turn the corner at Sixth Avenue (36-40)
The speaker depicts himself and the musicians (with all their instruments) as one big group. They're all doing the same thing: angling over to the south side of the street. They're moving together. What's more, the speaker refers to them as moving in their "own tightly knit way." The use of the words "tightly knit" suggests just how close this "group" is. They're tight buddies.