in_cube is a Winamp plugin intended to play streamed audio formats found in Nintendo Gamecube games video games.
For info on what games are supported, check out the publicly-editable GC Stream DB
Currently it supports:

• ADX (with looping for “03″ and “04″ versions)
• ADP a.k.a. DTK (only playback at 48KHz Stereo) – note that some games (Battalion Wars) have the ADP extension for DSP files, these will be recognized as DSP
• DSP variants:
  • standard (including simultaneous playback of left and right channel files as stereo)
  • “RS03″ (Metroid Prime 2)
  • SPT/SPD (Bust-a-Move 3000, Hello Kitty Roller Rescue) (only for single songs, not banks)
  • “Cstr” (Star Fox Assault, Donkey Konga)
  • STM (Paper Mario 2, Fire Emblem) – must be renamed DSP to not interfere with winamp’s support for another format called STM
  • HPS (HALPST) (Super Smash Bros. Melee, Kirby’s Air Ride, Killer7, etc.)
  • IDSP (Super Mario Strikers)
  • MSS (Second Sight)
  • GCM (Lego Star Wars)
  • Monopoly Party’s screwy single header stereo – must be renamed .MPDSP
  • ISH/ISD (Pokemon XD)
  • YMF (WWE Wrestlemania X8) – most files work
  • RSD (RSD3GADP type)
  • IDSP (Harvest Moon)
  • GCub (.wav) (NHL Hitz Pro) – must be renamed .dsp
  • WAM/WAA/WAC/WAD (Beyond Good & Evil), a RIFF variant
  • WVS (Metal Arms)
• 16-bit big endian PCM
  • RSD (RSD2PCMB and RSD3PCMB)
  • AST (Mario Kart: Double Dash, Super Mario Galaxy)
  • WHD/WAV (Hitman 2)
• AFC
  • “standard” (Wind Waker)
  • AST (Twilight Princess)
• RSF (Metroid Prime) – experimental
• Playstation ADPCM (not used on GC, but…)
  • VAG
  • ADS
  • NPSF (Ace Combat 5)
• a bunch more I need to add to this list…

If you were using in_dsp or in_adx you should remove them before installing in_cube.