Whilst I do not have an MS Media Centre, I do have a good knowledge of the Lintronics box and I have one sat in front of me which I use for various tests.
The Lintronics box is very flexable and some may say to flexable because it is able to translate almost (99%) of IR codes to what you want. It has all the standard conversion tables and you can build your own. The negative is that it can be quite complex to setup for the first time, but once you fully understand the principles its fine