Both. It may be touched on earlier in the thread but I don't remember and here's more about it.
For both multichannel playback and for a 2-channel stereo mix-down the process of dialing everything in is the same, though the result of the choices are somewhat different. I level balance channels, sometimes eq balance them as well, and sometimes do some work on dynamics. I don't know how different exactly, since I've only made stereo mixes directly and never tried to sum a multichannel playback balance down to 2-channel. I start by getting a good left/right level balance alone, eq that if necessary. Then bring up the center channel (routed to it's own speaker or panned to stereo center) and adjust the center/sides balance and imaging across the front. I play around with it, listening at different balance settings. Depending on the recording, 'just enough center level', 'about the same level of center as left/right', and 'more center than left/right' might all be viable choices, and it takes returning to each and listening for a while to decide which of those I like best. For each of those very different gross-center-level choices, I usually pretty quickly home in on a preferable fine-level adjustment for each one of them. I don't know why and find that very interesting. A few dB makes the difference in things 'snapping into place' in each case, but the center level may vary by 10dB or more between the three primary gross level choices. Regardless, after a while it becomes evident which one is best. Besides imaging, center level provides some control over the reverberant balance and forward presence.
Last I bring up the rear facing mic(s). If mixing to 2-channel, I'll pan the single rear mic to center, or if I have a pair I'll pan them fully to each side or inwards somewhat if necessary to make it seamless, EQ that as necessary. The use and level of the rear facing mic(s) is probably the biggest difference between a 2-channel mixdown and multichannel playback, but I almost always use some in the stereo mix, if just enough to get a sense of depth, width and richness, just enough to make the room sound or audience more natural. Or I'll get fancy and automate it’s level, changing it between songs for great crowd reaction, sometimes between more sparse/quiet tunes and more sonically-dense/louder ones. Managing the rear channel level is far more important in a 2 channel mix than with direct speaker playback where I get the level and eq to sound right and leave it, unless something annoying happens back there.
The ability to tweak the center/sides and front/back balance after the recording has been made which makes the 4-mic setup very flexible and less dependent on getting stereo mic spacings and angles just right, but what I really like is the control over presence, sense of depth, and envelopment that lets me adjust those things for a seamlessness sense of naturalness.
Sometimes I'll go farther and EQ or compress the center differently than the sides and subtle adjustments there beyond the need for simple corrections can be really useful for imaging. Rolling off the low bass in the center mic sometimes helps clean things up and is one reason I'm not concerned about a strong low bass response from the small ATs or DPA 4098s I'm often using as center mics.
I play these back at home with something similar to a home-theater setup, but one used mostly for reproducing my multichannel recordings. Left, center and right mic channels to left, center and right speakers arranged in a wide equidistant arc across the front. If I lean back from the center of the couch I see something like a standard 60 degree angle between L/R speakers, if I lean forward over the coffee table they are at 90 degrees, and sitting normally they are somewhere in between. The rear facing mic channel is mult'd to 4 or 5 speakers around the back. The 8 speakers form an arrangement close to an equal sided octagon. All speakers are full range, with floor standers across the front and the matching one directly behind, with two dedicated surround speakers in the back corners, and two bookshelves to the sides, no subwoofer. The median line through the center of the playback arrangement is on a diagonal in the room. Most of the surround recordings from rigs in this thread are 4 channel, except the on-stage 5 ch stuff over in the on-stage recording thread. For the 5 channel recordings I use 5 or 7 of the 8 speakers.
Starting to work on a portable version with smaller out-door patio speakers clipped around a pre-wired pop-up canopy, a suitcase sub or two and a deep-cycle battery. Will be cool to pop-open in friend's backyards, and to be able to play the surround recordings back at the remote campsite above the banks of the Suwannee as I make them at that festival.