as I have tested successfully, you have 2 choyses.
the first is relatively expensive but very useful. if you can, borrow or buy also protocol converter from Optelec (support has ended) which introduce satellite displays to system as BC displays.
second is that you buy srs232 converter it means, if you have only usb ports on your pc, that you plug in usb side into pc and the other side of converter (serial called also rs232) connect with cable to alva's serial port. In this case you should use brltty.
remember: you must know on which com port a display is connected, so you can setup brltty. and if you use brltty, do not use usb connection on windows with this display.
hope it helps.
p.s. braille extender addon cannot help.