I remember being absolutely devastated when the U.S. Robotics 28.8k modem I purchased was too fast for the 9.6kb/sec speed the 8250 UART on my 386sx. I had to sell it to somebody else and find an expensive internal model with its own UART. I think later they started selling internal modems without UARTS that just used the CPU to do the work, I wouldn't be surprised if that was the case here.
He's saying get an _extra_ serial board (put it into an ISA slot) that has the 16550 on it. Back then, this was a common way to get around what you're talking about.
