If I can just add my 2 cents worth here. My buddy Terry makes analog summing mixers. They started as a DYI project.
Here is a statement he made on his website:
With modern DAW software, mixing within the computer has resulted in some great sounding recordings, but I have long been intrigued by the concept of analog summing. I was not prepared to pay $800.00 or more to test that theory, so I engineered and built my own. Then to test the theory, I set out to see if there was any difference in the mixed sound. Much to my amazement and pleasure, I did notice a subtle but very pleasing difference in the stereo separation and placement of the instruments compared to my In the Box mixes."
Q: Is analog summing going to make your recordings sound like a Nashville studio with a billion dollars worth of equipment?
Probably not, but you will notice a difference in your mixes using a summing mixer.