Edited version of standard Plex Chromecast profile which sets the music transcode target to WAV/PCM instead of MP3. Lossless files like FLAC will transcode in full quality (unless they have higher bit depth than 16bit due to s16le profile).

Chromecast.xml

<?xml version="1.0" encoding="utf-8"?>
<Client name="Chromecast">
  <!-- Author: Derek Fowler. -->
  <TranscodeTargets>
    <VideoProfile protocol="http" container="mkv" codec="h264" audioCodec="aac" context="streaming">
      <Setting name="VideoEncodeFlags" value="-x264opts bframes=3:cabac=1" />
    </VideoProfile>
    <MusicProfile container="wav" codec="pcm_s16le"/>
    <PhotoProfile container="jpeg" />
    <SubtitleProfile container="ass" codec="ass" />
  </TranscodeTargets>
  <TranscodeTargetProfiles>
    <VideoTranscodeTarget protocol="http" context="streaming">
      <VideoCodec name="*">
        <Limitations>
          <UpperBound name="video.width" value="1920" />
          <UpperBound name="video.height" value="1080" />
          <UpperBound name="video.bitrate" value="12000" isRequired="false" />
          <UpperBound name="video.bitDepth" value="8" isRequired="false" />
        </Limitations>
      </VideoCodec>
    </VideoTranscodeTarget>
  </TranscodeTargetProfiles>
  <DirectPlayProfiles>
    <VideoProfile container="mp4" codec="h264" audioCodec="aac" />
    <MusicProfile container="mp4" codec="aac" />
    <MusicProfile container="mp3" codec="mp3" />
    <MusicProfile container="wav" codec="pcm" />
    <PhotoProfile container="jpeg,gif,bmp,png" />
  </DirectPlayProfiles>
  <ContainerProfiles>
    <VideoContainer name="mp4">
      <Limitations>
        <Match name="part.optimizedForStreaming" value="1" />
      </Limitations>
    </VideoContainer>
  </ContainerProfiles>
  <CodecProfiles>
    <VideoCodec name="*">
      <Limitations>
        <UpperBound name="video.width" value="1920" />
        <UpperBound name="video.height" value="1080" />
        <UpperBound name="video.bitDepth" value="8" isRequired="false" />
        <UpperBound name="video.level" value="42" isRequired="false" />
      </Limitations>
    </VideoCodec>
    <VideoAudioCodec name="aac">
      <Limitations>
        <UpperBound name="audio.bitrate" value="768" isRequired="false"/>
        <UpperBound name="audio.channels" value="6" />
      </Limitations>
    </VideoAudioCodec>
  </CodecProfiles>
</Client>