sextet vs musical group

sextet and musical group both are nouns.

Word	Noun	Adjective	Verb	Adverb
sextet	Yes	No	No	No
musical group	Yes	No	No	No

As nouns, musical group is a hypernym of sextet; that is, musical group is a word with a broader meaning than sextet:

Other hypernyms of sextet include musical organisation, musical organization.

sextet (noun)	musical group (noun)
a musical composition written for six performers	an organization of musicians who perform together
six people considered as a unit
a set of six similar things considered as a unit
six performers or singers who perform together
the cardinal number that is the sum of five and one