Would it automatically use hardware flow control when just piping the data to /dev? The file might be bad cause you're experiencing buffer overruns. I know with Amiga Explorer it not only does flow control but will retry bad transmissions. I'm also stuck to a pretty low speed (19200-38400) on my A1200. But it does work and is pretty reliable.
It might be easier and more reliable as the previous poster mentioned to just use a simple terminal program on the Amiga size and sz (send zmodem) and rz on the unix size.
