Your figures are right for the OHMmage on teh amps, parallel and series. One thing I would check though is that in series, the second sub in the string is dependant on the first one. If the coil starts to go in the first, it might accelerate the frying of the other by sending screwed up signals to the OK coil. Also, I'm not sure if this applies here, but have you ever hooked up 2 light bulbs in series? The second one in the circuit is always dimmer. Plus, if one goes, the other will fall silent
