I have recently switched from an all PS2 solution to hybrid PS2/USB solution with no ill effects. Basically I had the following:

chained 3x Xkeys pro+1x Xkeys stick multicast to 5 computers
1 full PS2 keyboard+X key stick switched to 5 computers
4x Xkeys pro for individual control of computers 2-5 (one each) (this turned out to be rather unnecessary as there are no fights in BC that require completely individual play like in the scholomance end boss, but it is nice to have just in case).

I then added two XKeys foot pedals. One programmed to repeat holydin flash heal on tank the other repeats mage attack /castsequence. With one foot pedal broadcasting a repeating character things were ok but with two pedals the rest of the setup becomes completely unresponsive (basically it looks like there is a limit on how many characters can be sent over PS2 originating from multiple units).

So what I did is buy a bunch of PS2 -> USB converters from monoprice, two vetra USB broadcasters (one for trackball the other for the 3xmage /castsequence foot pedal) and five 4 port USB hubs.

I still have 8x PS2 vetra broadcaster and 8x PS2 vetra switch and that takes care of all the backend keyboard switching and xkey multiplexing for main control array. I then use the converter to connect it to the hub. Each hub receives:

1) PS2->USB converted output of the main switch+main multiplexer
2) Individual USB trackball (each computer has its own physical trackball)
3) Multiplexed USB trackball (only for computers 2-5)
4) PS2->USB converted foot pedal (left foot for computer 2, right foot multiplexed for computers 3-5).

I then have ONE USB cable going from the "big spaghetti" to each computer.

Overall this combines the advantages of PS2 (fast switching and multiplexing) with the cable clutter reduction and higher bandwith of USB. I am happy with the way it works and it makes the foot pedals much more useable

I program all three buttons on each foot pedal to the same thing effectively making them 1 button devices (trying to hit the small side buttons is just not practical with a foot so I ignore them). Each device is programmed to repeat send a key while held down (corresponding to flash heal/nuke cast sequence) and when released to send a /stopcasting macro key once (this way for example if the NPC throws up a reflecting shield all I have to do it take foot off pedal to stop casting and avoid reflect, same for healing for agro shedding bosses like shattered halls ogre boss).

Ziran