SoundField recently began shipping its UPM-1 stereo-to-5.1 converter.
The UPM-1 is a 19in rack processor designed to create 5.1 material from old program material, which only has a stereo soundtrack. Such legacy programming is a problem for companies broadcasting HD with 5.1 surround audio, because listeners find it distracting when HD shows are broadcast in 5.1 surround and then the audio narrows to a very flat-sounding two channels for older material.
The UPM-1 doesn’t work by adding reverb or using phase shifts to generate new material for the rear channels in a 5.1 soundscape; it adds nothing new to the audio at all.
All of the material in the 5.1 mix that appears at the processor’s outputs is derived from spatial information present in the original stereo signal. Additionally, the UPM-1's processing is adaptive, changing with the input signal, rather than remaining constant irrespective of input.