Taiphan- yes just follow the traces over to the input board, the USB data input is marked D+ & D-. Use an ohm meter to make sure which one is which and then solder to the upper backside pins on the input board. The other two wires on the USB are power and ground, the power wire is a direct connection to the yellow LED light on the front, myself I would not hook it up. Not sure if you need to hook up the ground wire, hopefully not. Why don't you do a little experiment for everyone and disconnect the power ... then the ground ... from the output of the Ultravox and see if the USB still works. After that it's just a matter of filing out a larger USB hole, mounting the Ultravox internally and hard wiring the D+/D-. Keep us posted.
Here is a picture of the input board with light shining through it so you can see all the traces. You can easily see the D+/D- USB input traces to the Tenor USB chips. Next to them is a separate ground wire for the 3.3V regulator for the Tenor chip and the HC157. The HC157 provides the output switching of the I2S from either the Tenor or Wolfson chip to the reclock board and ultimately the DAC chips. Its this separate grounding trace that I suspect cause havoc with the Spdif input/I2s output and the reason the IFU mod works so well.
If you look careful I have removed the Pulse transformer exposing the ground traces underneath. I cut the trace and removed the pin under the number 5 effectively moving the entire ground plane for the Spdif input circuitry over to my source ... IFU mod. (Primary on Pulse, 12Mhz clock, Wolfson Spdif receiver chip, 3.3v power regulator and 74H04 USB/Spdif logic chip). Tony and I have achieved excellent results by doing this but this will depend on how clean your source ground is. (Notice the secondary ground trace going down, it is still grounded to the same point on the main board.)
If you want to float "just" the Spdif input to the Pulse transformer, the original intention of the FIM (floating input mod) then this gets a bit more complex as the 75 ohm resistor to load the Spdif input is located on the back of the board. This is a "tiny" surface mount resistor and I had no luck moving it over to the secondary pad, which by the way Nugent says is the ideal location for the 75 ohm resistor. If you could get that done then a true FIM is easy; remove the 2 primary pins on the pulse transformer and bend it back away from the board, next solder the coax Spdif input wires directly to the primary leaving the board traces intact. There is a lot of controversy on how best to handle Spdif input, myself I always prefer the simplest and cleanest approach.
Here is a shot of the back side of board. The 75 ohm surface mount resistor is located under the b for bypass. If you are very careful you can move it over to the open secondary pad right next door. Another awesome solution would be to solder in a 75 ohm Z-foil resistor to this location or across the primary, your choice.
Here is a picture of the my friend Jay's Chameleon that I just got done installing the 47uf Blackgate FK's and .1uf Vishay Roderstein MKP-1837 film bypass caps. It was like a jigsaw puzzle getting them to fit in ... but they do fit! I started by wrapping the legs and soldering the film caps to the Blackgates. You will also want to remove both 10uf and .1uf factory installed surface mount caps before you solder down the Blackgates in the provided holes. The row of Blackgate's nearest the front do not have through holes so you must bend the Blackgate legs and solder to the pads where the 10uf caps were. (Leave the row behind this row open to provide easy access to solder these legs down first.)
In the past I used .01 MKP-1837 bypasses for the Blackgates, while they are easier to install the .1uf MKP's proved to be superior sounding. This is yet another Steve Nugent tip, every little thing makes a difference at this stage of the game.
Thanks again, Steve!
The DAC above is stock except for the Blackgates and bypass caps, one could leave well enough alone and enjoy there Chameleon doing nothing else. This is the by far the biggest bang for the buck IMO. Everything else is just Gravy!!!