As a practical matter, the CPU has to deal with IO as well, I don't believe any 486 systems could handle this.
DSP based systems struggled a lot with IO in the late 90s until faster SATA drives became ubiquitous. Lots of them used SCSI or exotic hardware cards to deal with large track counts.
The first version of Ardour was written on a 25Mhz 486 and could record 24 tracks of 24bit 48kHz audio without breaking a sweat.
It did have a SCSI drive, but in 1999 I did not consider that "exotic", having been using them on various Unix workstations for more than a decade before that.
