dumb as it sounds, with both CGMiner and BFGMiner you have to restart the miner for the ' new ' miner to use the clock settings.  I still recommend removing all but the 2 defunct ones from the system and trying just those 2, each on it's own USB chain or on different powered hubs.

I bought a cheap powered hub then found out it has the sideways mounts so I can only fit 4 miners on it AND they have power switches ( nice blue glow to show there is power going to the miners ).  I hit a switch while moving the hub and had to restart as when it re-detected the Ant, it was only getting 1GH/sec until I closed and reopened BFGMiner.  With the other one ' suddenly ' working, I'd definitly look at the cables and see if you can swap USB cables to see if it totaly clears things up.  Been there, Done that, got a USB B cable that only does power that came with a Pic18f4520 board  for powering it, they went cheap and didn't add the other 2 wires IN the cable but didn't remove the connectors at both ends so it looks good on the outside, just can't do more than power things with it.  Just saying, the cables may be adding to the issue.

Good luck with the resistor upgrade.  They DO GET REALLY HOT so, if you have some old/dead ATX power supplies, a drill and a hack saw, there are aluminum heat sinks waiting to get cut down to the right size for Ants...