iOS 6 Audio multi-route - use external microphone AND internal speaker simultaneously

// Provides audio samples from AudioSampleProvider property.
//  (MediaStreamType parameter will always equal Audio.)
protected override void GetSampleAsync(MediaStreamType mediaStreamType)
{
    // start the microphone capture if it's not started yet
    if (microphone.State == MicrophoneState.Stopped)
    {
        microphone.Start();
    }
}

// gets called back when the microphone's buffer is ready
private void microphone_BufferReady(object sender, EventArgs e)
{
    // Retrieve audio data
    microphone.GetData(buffer);

    // Reset MemoryStream object
    memoryStream.Seek(0, SeekOrigin.Begin);

    // Write the newly acquired data into the memory stream
    memoryStream.Write(buffer, 0, buffer.Length);

    // Send out the sample
    ReportGetSampleCompleted(new MediaStreamSample(mediaStreamDescription,
                                                    memoryStream,
                                                    0,
                                                    buffer.Length,
                                                    0, 
                                                    mediaSampleAttributes));
}

- (void) currentOutputs:(CDVInvokedUrlCommand*)command {

    if(!mpVolumeView){
        mpVolumeView = [[MPVolumeView alloc] initWithFrame:CGRectZero];
        mpVolumeView.showsVolumeSlider = FALSE;
        [self.webView.superview addSubview:mpVolumeView];
        [mpVolumeView setAlpha:0.01];
    }

    UIButton* btn = nil;
    for (UIView *view in [mpVolumeView subviews]){
        if ([view.class.description isEqualToString:@"MPButton"]){
            btn = (UIButton*)view;
            break;
        }
    }

    if(btn){
        [btn sendActionsForControlEvents:UIControlEventTouchUpInside];
    }
}

    do {
       if #available(iOS 10.0, *){
            try recordingSession.setCategory(.playAndRecord, mode: .default, options: .defaultToSpeaker)
        } else {
            AVAudioSession.sharedInstance().perform(NSSelectorFromString("setCategory:error:"), with: AVAudioSession.Category.playAndRecord)
        }
        try recordingSession.setActive(true)
    } catch {
        print("failed to record!")
    }