Get the C1000C+P. If you are going to "build" out the HT, don't bother with the MX150 (and waiting until mid/end of summer for it, either) just yet. Worry about it when you add a center and surrounds.
Also, don't go ghetto on a center, if you get the XRT1K's you need the XCS1K. Any argument you have for not getting that is invalid.
With the rate processors change and by the time you get around to going 5.1 (considering how AWESOME that 2-channel system will be), an MX151 or something like that will be out, and you can probably be able to pick up a used MX150 for "barato."
Don't forget 2x PPP's. And with the MCD500, just go ahead and get the MS750 or its equivalent (by the time you purchase) since you can use it through the DAC of the MCD - the convenience is wonderful and it will still sound wonderful.