interesting... i don't have a usb on my stb.... i've seen sites that teach you how to make a serial cable to control your stb -- i do have a serial type port on the back of my stb, so i think i could do that...
My STB doesn't have a serial port. All D* STBs are going to USB. A friend of mine gave me 2 serial adaptors, so I connected them to each end of a regular network cable , one goes in the back of the PC, the other connects to a netgear serial to USB adaptor, then the USB into the STB.
I control it with the directv.pl script that you can find online.
The hardest part is the script needs some module for perl loaded, so the script can communicate with the serial port, but again, you can find it online. I believe you still need this script for serial to serial.
If you are going to be streamming outside your home network, this is really cool because you can have a very small connection into your home network so you can change the channels without taking up bandwitdh that you can use for the actual streamming.