I never heard any that I liked in the digital domain, but I had a McCormack MAP 1 multi channel anlog preamp that has so called Ambience Retrieval Mode (ARM) which works like a charm. The Conrad JOhnson MET1 has the same feature.
Which surround algorithm is better?
I know this is a controversial topic. I know that there are those that only would listen to two channel and never to music in multi-channel. This question is not for you. I understand both sides of the issue. I have found that my room, which is 17' wide at the front, and 25' deep from front to rear (and I sit half way back) cannot reproduce a full symphony-like sound from my two speakers. They are VSA VR-4JRs and I like them for most everything I listen to. I have been experimenting with different surround processes and have found that some of the recordings sound more like a full symphony with some of the processes and others do not. Right now I am limited to the algorithms from my receiver, an Onkyo 805. I prefer the well produced SACDs and DVD-As but most of my music is in CD form. I am lucky enough to listen to the St. Louis Symphony in the beautiful and acoustically astounding Powell Hall, so I have real comparisons. My question is directed to those who have experimented with various algorithms. Which ones in your systems have come closest to the real thing in your rooms when changing two channel CDs into multi-channel? Which processes and processors do you like, especially for full symphony orchestras? Thanks.