The best replacement for line in is mic in.

The best alternatives to line in are rated as following:
★★★★★  mic in
★★★★  microphone
★★★  line out
★★  lfe
★★  phono
★  mic
★  aux in
★  microphone jack
★  microphone input
★  lfe subwoofer
★  insert
  aux
  microphone in
  mic jack
  stereo mix
  lfe in

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Speaking about line in, one probably shouldn't forget about sonos.

Other search terms related to line in and their ratings are:
★★★★★ sonos
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line in
mic in
microphone