Yea as Dave and Dean say above.  a summing mixer does some or most of the summing in the analog world, as opposed to all digital.  The D box has only 10 analog inputs (8 plus an alt input, if I remember right), which could be broken down any number of ways.  10 mono tracks coming out of your interface, or if you have more tracks than DAs you can stem them.  One guy even did his stemming by frequencies - kick and bass and floor tom in one mon, cymbals and other metal perc in a stereo, etc.

The purpose is relieve the supposed internal digital distortion/problem/etc. when summing.  Theoritically, it is funny since "analog summing" came into vogue as digitial summing was using more and more bits to bypass such supposed limits.  Even ProTools jumped to 48 bits, and that was the supposed program that had the problem in earlier incarnations.  I suppose it is in the ear of the beholder, like higher sample rates.  I do 44.1, and most studios do too that I know of.  But no less than Rupert Neve said he thought sample rates were too low.  And I ain't going to argue "sound" w/ him, but I continue to use lower sample rates.

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