No problem, all here to share info. What do you want me to explain?.
Serial only flash are are done with NFI images and VTI Util. I've done this in the past and it does work. The downside of this is that not many teams produce images in NFI format anymore, 99% of them do usb only. However, during my recent mission to restore a box I discovered that when you build an openpli image, the built process also produces an update to date .NFI image too.
Serial Guide
http://www.world-of-satellite.com/showthread.php?18-VU-Utility-and-guide-for-usage-of-the-VuUtility
As for the I2C/JTAG method thats also documented many many times on many sites. I'm more than happy to talk you through too if you want. It involves buying a USB programmer that will interface with the Broadcom SoC in the STB. That SoC connects with 4 jumper wires via a pin header on the PCB (GND/3.3V/SDA/SDL) to the usb programmer and you need to use BBS3 (Broadcom studio) to program the (possibly blank) Nand with at the very least the CFE if you can use the USB interface to finish the job (which is quicker), or you can just program the whole nand this way.
I've done a VU UNO this way but its pretty similar for a DUO/UNO and probably other machines in the range, the only thing that differs is the pin header layout.
Please LMK if you need to me explain any part of this in detail. I'm more than happy to impart what I know.
I documented my travel replacing my nand in my UNO on another site and did point to that in one of my posts on here, but I'm open to helping anyone I can with any questions.
BBS3 + PDF on how to wire things up.
https://www.dropbox.com/sh/nk7u7dcx62lsetz/nBKi6byn3P/VU Tools zum Wiederbeleben JTAG.rar
You know what
If i get time, this weekend I'll do a write up of the process. There are COUNTLESS tutorials on the interwebs on how to do this though, thats how I learnt
Unless you are talking about the network based flash?. I've never done that but interrupting the boot I saw that the CFE did support flashing and it appeared to support tftp baed flashing. I've only JUST recovered the box and am not in the mood to play with it, just stating that it appeared to support it. I have done the other two methods (serial/i2c) personally, so if his USB port is dead, there are options.