sentence stress vs emphasis

sentence stress and emphasis both are nouns.

Word	Noun	Adjective	Verb	Adverb
sentence stress	Yes	No	No	No
emphasis	Yes	No	No	No

As nouns, emphasis is a hypernym of sentence stress; that is, emphasis is a word with a broader meaning than sentence stress:

sentence stress: the distribution of stresses within a sentence
emphasis: the relative prominence of a syllable or musical note (especially with regard to stress or pitch)

Other hypernyms of sentence stress include accent, stress.

sentence stress (noun)	emphasis (noun)
the distribution of stresses within a sentence	intensity or forcefulness of expression
	the relative prominence of a syllable or musical note (especially with regard to stress or pitch)
	special and significant stress by means of position or repetition e.g.
	special importance or significance