Stanza 4 Summary

Get out the microscope, because we’re going through this poem line-by-line.

to Tommy Potter for taking the time
to join us on this breezy afternoon
with his most unwieldy bass

Here the speaker refers to another jazz great, Tommy Potter, a bass player who used to play in the band of the famous jazz musician Charlie Parker. The speaker speaks about Tommy Potter figuratively, as if he's stepping alongside the speaker and Rollins on the pavement.
In other words, the speaker doesn't say, "I'm listening to Tommy Potter play the bass now." He says that Potter is "taking the time/ to join us on this breezy afternoon," which makes it sound as if Potter is literally joining or walking along with the speaker and Rollins.
The way that the speaker describes listening to the music here is important because it evokes a sense of community. The speaker isn't alone. He's keeping company with these jazz greats, and they're keeping him company. They're one big happy family.

and to the esteemed Arthur Taylor
who is somehow managing to navigate

And here's another musician who is joining the speaker's jazz parade. Arthur Taylor is a famous drummer who helped define the sound of jazz in the 1950s and 1960s, and now the speaker is listening to him too.
The stanza cuts off in the middle of a sentence here. The speaker is telling us that Arthur Taylor is "somehow managing to navigate" something, but we don't find out what that is until the next stanza. So let's hop on over there.