i transplanted my x-arcade 2 player panel components into a panel i built. i added a 3" wico trackball (mousehack) and hard drive spinner (mousehack). the problem you will run into with the x-arcade is the wiring. the stock wires are very, very short, so if you are moving the two players further apart, you will need to extend the wires to one of the players controls...it is a pain in the *** if you are trying to keep all of the stock wiring intact. if you don't mind cutting and splicing it will work out OK. I am just about to build a new panel for mine again to add a little room the dedicated 4way stick and the spinner, but once again my wires are not long enough..so this time I am going to buy an ipac and redo everythign the right way. the other thing to know about teh x-arcade interface...unlike the ipac, ground is not ground. buttons are divided up into groups of 4, each group has it's own ground. if you use a ground from one group on a button from another group, those buttons don't work like they are supposed to...i found that out the hard way and had to rewire a bunch of stuff after my panel became basically unusable for a while.
looking back, if i were going to do it all over again (and i am) i would have saved up a little money for an ipac or keywiz and done it right the first time. then I am going to put my x-arcade back together and use it to play metal slug anthology on my Wii.