edit: northerngames posted while I was typing this, but I had written too much to want to go back and see if any of my information is refuted by his . . .
As I understand it, the FTP server has to be part of the chip. For example, SmartXX was the first chip to have a built-in FTP server, followed later by Xenium. The Xenium actually beat SmartXX to market by a long way, but it didn't have FTP until after SmartXX introduced the feature and it was added later in an OS update. Similarly, the Xecutor 2 chips did not (do not?) have built-in FTP. They were around for a LONG time before Xenium and SmartXX.
The thing is, all of these chips, from day one, have been loading hacked BIOSes. If FTP was in the BIOS, why would SmartXX, a company that doesn't even deal in BIOSes (you use an Xecuter or Evox bios with this chip), or Xenium, who is in the same boat, be the first to incorporate FTP into their chips if the FTP is part of the BIOS? It doesn't make sense to me that you could even change the BIOS that much, add something that big, without breaking it. The BIOS is the lowest-level layer of software that acts as an intermediary between the software and hardware. It seems unlikely to me that they could fiddle with the MS BIOS that much. I think they basically do nothing to it aside from stripping security routines out of it and adding very basic things, like the ability to reset the box with a specific combination of button presses (basically adding CTRL+ALT+DELETE).
The giant leap forward in the 3rd generation of Xbox mod chips was the addition of an onboard OS. All the modchips before that had memory banks that could load hacked BIOSes, but the addition of an onboard OS, allowed the chip to run its own software, which is what gave us the ability for the chip to have things like HDD utilities and applications like FTP and web servers.
So, I might be wrong, but that's how I understand it, and why I believe that the DuoX2 might possibly not have an FTP server. I know that with a SmartXX, Xenium or Xecutor 3 (the only chips I have personal experience with), I can FTP into my box before ever transferring a hacked BIOS to it. And, for that matter, before ever loading any BIOS at all (hacked or otherwise). When you have one of these chips, you load into their configuration screens (their OS) before the BIOS is ever loaded. From there you can select what BIOS you want the machine to load. Also, at this point, before you have ever selected which BIOS you want to load, you already have access to the FTP server.