Hi Chris,
Could you check your output device in the Preferences dialog? You might need to enable the correct device to properly hear all channels. For example, if you’re using headphones you might want to enable Windows Sonic.
Also, could you let me know how you can tell it is being summed to stereo? Are there multiple channels showing metering in the tracks/master bus? Check what the current project’s build is set to as well.
Thanks,
Richard