You can use CSCore to do that:
private static void Main(string[] args)
{
using(var capture = new WasapiCapture())
{
capture.Initialize();
using(var source = new SoundInSource(capture))
{
using(var soundOut = new WasapiOut())
{
capture.Start();
soundOut.Initialize(source);
soundOut.Play();
Console.ReadKey();
}
}
}
}