Been a while, but you should be able to just open up Telenet and let the M1/XSP do it's thing and you should be able to see what is passing through the XSP to the serial.
IMHO, unless you're 100% sure you have a USB to serial that is bullet proof and works 99% of the time, don't assume anything, I have a backpack of at least 5, if not 10, serial to USB adapters up to ridiculously expensive that work with some hardware and not others, while a dedicated serial picks up everything all the time.