pretty sure Vetra has something of what your wanting. Cant remember exactly what it was but it allows you to use multiple mouse in front of your KVM switch. I couldnt get mine to work because it will not convert USB to PS/2. Has to be PS2 all the way. Call Vetra to get the one that doesnt have any delays on it. They special made an order for one of us boxers to not have that delay in it. I got one of those they had made. Currently not using it as intended. But it sounds to me this is what you want to do. Have multiple devices hooked up...Xkey..mouse...keyboard then KVM switch...
example
XKEY..........
mouse........
keyboard.....
................4PORT switch???.....................dont remember what they called...just explain to Vetra what your wanting to do..be sure to also tell them u .................................................. ......dont want any delays in it
................KVM switch
.............................PC1
.............................PC2
.............................PC3
.............................ETC