https://gist.github.com/aetos382/e737286380e99cfaf9e8 を無駄に関数化してみたっす

Play-SpeechText.ps1

function Play-SpeechText {

    [CmdletBinding(
        DefaultParameterSetName = 'Default',
        ConfirmImpact = [System.Management.Automation.ConfirmIMpact]::Medium)]

    param(
        [Parameter(Mandatory)]
        [string] $ApiKey,

        [Parameter(Mandatory, Position = 0)]
        [string] $Text,

        [ValidateSet('show', 'haruka', 'hikari', 'takeru', 'santa', 'bear')]
        [string] $Speaker = 'show',

        [ValidateSet('happiness', 'sadness', 'anger')]
        [string] $Emotion,

        [ValidateRange(1, 4)]
        [int] $EmotionLevel = 2,

        [ValidateRange(50, 200)]
        [int] $Pitch = 100,

        [ValidateRange(50, 400)]
        [int] $Speed = 100,

        [ValidateRange(50, 200)]
        [int] $Volume = 100,

        [Parameter(ParameterSetName = 'OutToFile', Mandatory)]
        [string] $OutFile,
        
        [Parameter(ParameterSetName = 'OutToFile')]
        [ValidateSet('wav', 'ogg', 'aac')]
        [string] $Format = 'wav')

    $token = [System.Convert]::ToBase64String([System.Text.Encoding]::ASCII.GetBytes("${ApiKey}:"))
    
    $headers = @{
        Authorization = "Basic $token"
    }

    $body = @{
        text = $Text
        speaker = $Speaker
        pitch = $Pitch
        speed = $Speed
        volume = $Volume
    }

    if ($PSBoundParameters.ContainsKey('Emotion')) {
        $body.emotion = $Emotion
        $body.emotion_level = $EmotionLevel
    }

    $params = @{}

    $outToFile = $PSCmdlet.ParameterSetName -eq 'OutToFile'

    if ($outToFile)
    {
        $params.OutFile = $OutFile
        $body.format = $Format
    }

    $response = Invoke-WebRequest -Uri 'https://api.voicetext.jp/v1/tts' -Method Post -Body $body -Headers $headers @params

    if (!$outToFile) {
        $player = New-Object 'System.Media.SoundPlayer' $response.RawContentStream
        $player.PlaySync()

        $player.Dispose()
    }
}