Having the unused wire of a pair grounded helps shield the signal carrying wire. Ground them at the drive end only to "encoder minus".
You mentioned on the "geckodrive" group the LEDs are dimly "on" while the motors are running. I looked at your ERR/RES circuit but could not make out the resistor size. If they are 10K or less, the LEDs will be partially on. That should be no problem though.
A bad STEP/DIR cable can cause problems like that as well. The drive may be faulting because it is seeing a burst of noise pulses it stupidly thinks are steps. Try gently wiggling the cable. See what the effect is.
Mariss |