The best replacement for quartet is trio.

The best alternatives to quartet are rated as following:
★★★★★  trio
★★★★  apollo
★★★★  symphony
★★★★  expo
★★★  ensemble
★★  ucx
★★  quartet
★★  string trio
★★  symphony apogee
★★  duet
★★  string quartet
★  rme
★  rme ucx
★  duet 2
  forte klipsch
  mbox pro
  jazz quartet
  heresy
  uad apollo
  quintet

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Speaking about quartet, one probably shouldn't forget about asha bhosle.

Other search terms related to quartet and their ratings are:
★★★★★ asha bhosle
★ laurindo almeida
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quartet
trio
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