I am not arrogant enough to self identify as a DSP expert but I dabbled in DSP and crunched a lot of microcode. Inside the digital domain some things are easier than others. Summing is a relatively easy one clock tic add. Fader moves are likewise a one clock tic multiply. EQ is a little more complicated with coefficients that can be difficult to represent using fixed point with enough resolution to prevent issues.Are you summing 32 stereo busses? Also, are you processing the groups or just doing ouboard summing to avoid the DAW mix bus?
Maybe a DSP expert can offer info as to whether track count in a DSP mixer affects its behavior in any meaningful way.
Modern processors have become massively faster than decades ago. One potential track count concern is are there enough clock tics available to perform all the math operations within one audio sample (tens of microseconds).
The designer/coder should do this math before you encounter limitations.
JR
Truthfully, my clients in all genres seem to prefer in-the-box mixes better than when I is summing. This even goes for pop, rock, r&b, jazz, folk, and classical music. When I sum I always mix with the summing setup before I start so my decisions are based on what I hear.