Feast your ears, friends. This is a poem about poetry, and more specifically about meter. Poetry is all about sound, and this poem knows it. While the speaker doesn't talk about sound so much in the first stanza, in the second, he reveals the importance of "sound sense" in the making of a poet. Plus, he totally displays his own "sound sense" in the form of a regular rhyme scheme and things like alliteration and assonance that pop up all over the poem.
Lines 9-10: the speaker compares the amphimacer to a "thundering…racer." He uses "like" to make the comparison, so this is a simile. The amphimacer is loud, like thunder!
Line 14: The phrase "sound sense" has two possible meanings – it means both "good sense," and also "a good sense of sound," as in, a good ear.