Because I'm a degenerate, I most often sleep on my couch, which is conveniently located within my surround listening area. Generally, I fall asleep to music AirPlayed from my phone at very low volume, usually just shuffled from my synced library (excerpted from my very large ripped Apple Music library). It's predominantly classic and progressive rock, but it contains everything from bluegrass to classical to hip-hop to jazz and beyond. I leave the AirPlay/HEOS input on my Marantz set to Multichannel Stereo, which doesn't do anything special as far as upmixing, but just duplicates the L and R channels to their respective Ls and Rs channels in my 5.1 setup. I believe it also populates the C channel with a sum of L and R, and I keep bass management on, so the Sub handles frequencies below 80Hz. Normally, listening at a barely perceptible level would result in an extremely bass-shy sound due to psychoacoustics, but Audyssey's Dynamic EQ does a wonderful job of keeping the sound full and balanced.
When listening at more normal volumes and sitting in the MLP, even this most basic algorithm can produce some surprising "surroundy" effects. It just depends on how spacious, sparse, and "widescreen" the stereo mix is. I've had moments where I thought I accidentally changed the setting to a true upmixer, but no, it's still on Multichannel Stereo. If you have a Sound United (Denon/Marantz) AVR or pre/pro—or any brand that has some form of all-channels stereo, really—give it a try on some of your favorite stereo tracks to hear how they sound. You might just be pleasantly surprised!
