Best "pseudo" multi channel from 2 ch sources

As a HT novice I would very much like some guidance as to which AVR's/Processors are known for their ability to make a 2 ch source sound really good at a high end level? I find rear channel added ambiance to be enriching to the listening experience.In my case most of the source material will redbook cds. Also is a center channel speaker imperative for this scenario? Any guidance will be appreciated.
Meiwan wrote: If you are playing redbook cds mainly, the centre/rear channels will just be duplicates of the 2 main channels.

Not so. There are many systems that will extract ambiance information for surround and interpolate a center and these include the ubiquitous Dolby and dts processes. However, the OP is advised to try them before buying since they vary considerably in their capabilities and configurabilities.

IMO I have found no processor that surpasses the Angstrom 200.
I have the Anthem d2v processor, but for 2 channel sources I still use my Angstrom. It provides a fuller sound stage than just 2 channel alone. It also produces great 2 channel as well. There was one listed on AGON a day or so ago. PS, I have a $2000 DAC that does not out perform the Angstrom!! However, this unit a ten years old does not have the latest bells and whistles, but for DTS and 2 channel surround, it excels.
Either the Spread Spectrum Technologies Trinaural processor or the Miles Tech M86 (5 channel) or the M44 (3 channel) processor will do what you want using a 2-channel source. Both of these are analog domain processors; no need to go digital if you don't wan't to.

Full disclosure: I'm selling a Miles Tech here.
In HT, the center does more work than any other channel. The rears do the least. You can get away without a sub if your mains can handle the work.
I ahve an Emotiva UMC-1 preprocessor ($699 brand new with 5 year warranty) and it does a very good jo of synthesizing multi-channel from 2-channel sources. Just engage either Dolby PLIIx (Music or Movie) or DTS:NEO6 and have at it. Both of these can sound quite good with a proper source. I have found the effects to be quite pleasing and well worth a listen.

However, the UMC-1's DSP modes (Stadium, Hall, CLub, etc.) sound like real crap, zI never use them.