I share your frustration in the lack of information about EA, I will add my little knowledge to the pot and hope it helps.
I was warned never to cross a pair of electrodes over the heart, this will interfere with the hearts own electrical rythym and never use EA on someone with a pace maker as it can stop the device. Never use on broken bones (unfused) as this is extremely painful.
I read that for best results your machine must be Bi-phasic - this means that the pulse is equal on both needles, otherwise you will not achieve de qi. the pulse width should be 0.1 - 1.0 ms, square wave pulse 25-50 v 2.5 - 5mA at pulse width 0.1 ms if any one can tell me what this all means I will be greatful.
4 hz releases endorphins, 50 - 200 hz releases seratonin 2 - 4 hz is best to achieve de qi. high intensity to sedate, low intensity to tonify.
Generally you can use EA on any ailment to amplify the effect of the needles but I am wary of using it on patients with deficiency syndromes, moxa would be more appropriate anyway - maybe this is why you caused more pain in your client. muscle spasm is another concern, turn the intensity slowly and only to a tolerable level. I was taught that as long as you connect the electrodes to the needles along the line of pain, it will clear the channel and sedate the nerve.
As for the pain element and shutting down the nerve messages this is concerned with the gate theory, which you can look up in good A+ P books.
EA also stimulates nerve function and growth I was recently informed by an electro-physicist that the stimulation causes a chemical change in the synapse which affects the nerve cells on a chromasomal level and stimulates regrowth - this is why it is so effective for atrophy and nerve damage.
He also made me aware of the risk of using not only EA but any electrical device around any high output of magnetic radiation, this would mean mobile telphone masts, broadcasting stations, medical equipment such as scanning machinery. Basically the EA machine will act as an amplifier and can cause burns and tissue death, the difficulty here is being aware of the location of these types of radiation, but considering the extreme effects I think you would notice if this was happnening.