Just noticing this a couple years later .
There definitely is such a thing as a 32 channel SMF! With type-1 SMF, this is done using track/port assignment meta events.
It is also possible to assign more than 32 channels, should the target device support it, such as the MU128 and later or SC-8820/50 devices. These utilize the serial to-host connection or USB to access the full range of internal ports. Some of the official demo midi files for Yamaha's MU devices use all 4 ports, but this is otherwise fairly rare, to my knowledge.
It seems like there have been multiple methods used to assign the ports, here is a little write-up on the topic:
It would be very cool to have support for multi-port midi files in QMidi! Personally, I have quite a few of these, and have created some myself, but the options for playing them are pretty limited on a mac. Would be happy to share some example files if it would be helpful.
This web-based player supports 4-port playback: