The Furman system (and also the Hear Technologies) not only pass analog audio through cat-5, but also DC. I have found the cat-5 to be an incredibly crappy connector to use for this purpose, but much to my chagrin it seems to be gaining in popularity. Once those little plastic tabs pop off the connector, bad things start to happen, especially if you have headphone plugged in. The power gets intermittent and loud pops go to the cans, distortion, single-endedness, etc. El yucko!
Also, while I'm pooping on the Furman system, the mic-stand mounts they supply, with the velcro, are very unreliable. I actually disassembled the mixers and drilled holes in the bottom of them (and you do have to take the entire thing apart to do it) so that I could put tie wraps through the mixers to more permanantly affix the mixers to the mounts.
This is not as trivial as it seems, because it is easy for the mixers to take a spill. If they land the wrong way and bend the shaft of the pots, again, bad things start to happen.
Not a fan of the Furman system, can you tell? The Aviom seems very cool, but only drives one pair of headphones, and each mixer requires a power supply - but then, it is more than just a cue system.
Noah