The best replacement for subsonic is supersonic.

The best alternatives to subsonic are rated as following:
★★★★★  supersonic
★★★  plex
★★★  audiogalaxy
★★★  madsonic
★★  ampache
★★  high velocity
★★  nhibernate
★  infrasonic
★  supersonic 300 blackout
★  standard velocity
★  supersonic rounds
  serviio
  orb
  mpd
  tpg 1 pro
  remington subsonic

Your alternative for subsonic is not listed? Suggest!
Speaking about subsonic, one probably shouldn't forget about suppressor.

Other search terms related to subsonic and their ratings are:
★★★★★ suppressor
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Google Trends

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subsonic
supersonic
plex