i’m assuming you’re talking about the madcatz fightpad? here is the guide to the PCB:
this thread will help you out, particularly the second page.
edit: after reading more specifics on the Ultimarc website and seeing some installation photos such as this (the USB end isn’t attached to anything), it looks like you might not even need a PCB. the Ultimarc actually has an input on the stick itself, and they sell a wiring harness that lets you attach up to eight buttons to the stick, while the USB output goes straight to the computer. this could potentially work on an xbox, i would try this first. if it doesn’t work, you will have to go the soldering route.
more info from http://retroblast.arcadecontrols.com/reviews/Ultimarc_Ultrastick_0925006-01.html :
"There is an auxiliary connector on the UltraStik that can be used in input mode or output mode. Input mode allows you to connect up to 8 buttons and these buttons will be reported as game pad buttons to the PC. This feature can save you from requiring a keyboard encoder, or allow you to use one with fewer inputs on it. Ultimarc offers an optional prewired harness for this purpose.
Output mode allows you to connect the UltraStik to a keyboard encoder or actual arcade hardware. This allows the UltraStik to be used on hardware where a USB port isn’t present or perhaps on software that does not support a game pad. If the emulator you are using handles a game pad poorly, it allows you to report keystroke directions like a traditional switch based joystick if you have an encoder. The same harness for input mode can be used for output mode too. Note that you can’t send maps or configure the joystick when it is hooked up via output mode only (no USB). You would need to configure it first using USB, and then put it in place on a system without USB."