You're welcome.
No, it is the other way around--you only need a regular USB cable to connect to the back of the K5, which would send USB audio signals into the K5. This signal is forwarded to the X7 through the dock, (or X3II / X5II / E17K) for the docked device to decode. The resulting analog signal is sent back out from the docked device into the K5 through the extra pins in the 11pin "micro USB" dock back to the K5 for amplification. Thus if you use a regular USB interconnect / extension cable here you'd get no sound out of the K5.
I am quite sure of this because I was working for FiiO when the K5 was launched and translated its manual and promotional material.
While we're at it--make sure not to connect the USB cable from the computer / smartphone / HiFi / whatever to the micro USB "Dock In" port at the back instead of the large USB In port next to it. As explained above the dock port (of which there are two, one at the top, one at the back, only difference is one is male, one is female) is designed to forward, i.e. output USB digital audio signals to e.g. the X7. The K5 is liable to go kaput if you feed a USB digital audio signal *into* the dock port at the back. There may or may not be a warning sticker about this on said micro USB Dock In port at the back.
Thank you again for your kind attention.
I'm using K5 exactly as you described: I connect my Fiio X7 in the top docking and plugo the USB cable into the "USB IN" back, which connects to my computer. Everything works perfectly in this way: I put Fiio X7 in DAC mode and broadcast the music from my computer to the dock.
My problem is that I use a protective cover on my X7 Fiio, and every time I want to use it connected to K5 I need to remove the cover.
The back door micro USB K5 called "DOCK IN" is precisely to this kind of situation, is not it? Everything would be as it is (port "USB IN" connecting the K5 to my PC), but instead of plugging my Fiio X7 in the top docking, I would plug it in "DOCK IN" using a micro usb cable.
This is how it works, right? But where I can find a micro USB cable 11 pin with two male connectors?
I'll post some pictures that I think will help:
a) This is the way I use the Fiio X7 (DAC mode) plugged into the K5. Notice that I remove the Fiio X7 protective cover of Fiio X7 for plugs it to the top dock. My PC is connected to K5 through "USB IN" port.
b) I use a protective cover on Fiio X7 it impossible to fit the upper dock. In order to not have to remove it constantly I'd like to be able to connect the FiiO X7 not through the upper dock, but through the door "DOCK IN". But the problem is that the cable supplied with Fiio X7 is not compatible.
c) Alternatively, I wonder if I can use an adapter that converts the micro USB port to USB standard. I still have not tested for fear of causing a problem to the device.
That is my biggest question: I can do this?
This is the adapter cable:
http://www.ebay.com/itm/MICRO-USB-CABLE-MALE-HOST-TO-USB-FEMALE-OTG-ADAPTER-ANDROID-TABLET-PHONE-PDA-PC-/321955491110
Thanks again for the help!