So I had to do

modprobe ftdi_sio product=0x8350 vendor=0x0403 to make the usb serials arrive in /dev/ttyUSBx

then I had to modify /etc/systemd/system/multi-user.target.wants/cgminer.service

Changing

ExecStart=/usr/bin/screen -dmS cgminer /opt/minepeon/bin/cgminer -S auto --api-listen --api-allow W:172.0.0.1 --sharelog /opt/minepeon/log/share.log -c /opt/minepeon/etc/miner.conf

to read

ExecStart=/usr/bin/screen -dmS cgminer /opt/minepeon/bin/cgminer -S /dev/ttyUSB0 -S /dev/ttyUSB1 -S /dev/ttyUSB2 -S /dev/ttyUSB3 -S /dev/ttyUSB4 -S /dev/ttyUSB5 -S /dev/ttyUSB6 -S /dev/ttyUSB7 -S /dev/ttyUSB8 -S /dev/ttyUSB9 -S /dev/ttyUSB10 -S /dev/ttyUSB11 -S /dev/ttyUSB12 -S /dev/ttyUSB13 -S /dev/ttyUSB14 -S /dev/ttyUSB15 -S /dev/ttyUSB16 -S /dev/ttyUSB17 -S /dev/ttyUSB18 -S /dev/ttyUSB19 --api-listen --api-allow W:172.0.0.1 --sharelog /opt/minepeon/log/share.log -c /opt/minepeon/etc/miner.conf

I note the scale of the graph reports Th not Gh.

Cheers