I'm not interested in analog summing myself, but I think you're missing the point. It's not about "better" summing. You want more euphonic summing. Analog audio processing often comes with artefacts that give the signal sent through it a more pleasing character, for whatever reason (phase shift, saturation, channel differences between left and right, transient modulation, slew rate, power sag, etc.).

I personally think analog summing is a waste of time, because the differences are too subtle to be worth the investment in setting it up. But that's just my opinion. Some people are really into it (Eric Valentine comes to mind).

Just wanted to point out that in the context of audio equipment (both professional and audiophile) "sounds better" often means "sounds worse but more engaging". Just like a polaroid picture often evokes more emotions than a photo taken with a modern digital camera and a great lens.