You could certainly split the coax and use a separate MoCA adapter for the Xbox 360, rather than the MoCA adapter/switch setup I proposed.
I'm not saying you can't use DECA, as you suggest. You'd need a second DECA adapter to bridge the DECA segment back to Ethernet on your router* -- but your main roadblock would be ensuring that the DECA network doesn't step on your TV signals feeding your DVR(s).
Hopefully HarperVision will step-in and offer you some hands-on advice, as he's running DECA w/ his TiVos, I believe.
More info on DECA & MoCA:
MoCA and DECA – What’s the Difference? Or Is There One At All?
* p.s. You haven't mentioned how you're creating your MoCA network, to which you plan on connecting the Mini & Xbox 360.