No current MPEG-2 only box will be compatible with the new MPEG-4 streams. At least any time in the foreseeable future. The new MPEG-4 streams are on new satellites, that the existing MPEG-2 boxes are not aware of. If you wanted to convert an existing MPEG-2 box to receive these streams, you would not only have to change out the video procesing unit, but you would need a new satellite tuner unit in the receiver as well. This would not be cost effective or reliable.
The H20 is the only box currently capable of MPEG4 and 2, all other boxes are MPEG2 only.