LFE stands for 'Low Frequency Effects' (maybe you didn't know that, a lot of people don't) but the key word is EFFECTS. The single LFE signal has been 'processed' (as set by YOU) at the receiver/processor. IOW, with the LFE signal, the L and R channels have already been combined, the low pass frequency has been established, and often other parameters have/can be set (again, by you, from the menu on your A/V processor) depending on the features available on your processor. When you are playing 5.1 or 7.1 surround, the 'point one' subwoofer signal is "good to go" -- meaning that none of the controls on the sub itself are operable (except level) when using the LFE input. If you "process" everything you listen to (including two channel material) into surround sound, then you should only be using the LFE input regardless of the brand/model of sub.
The L and R single ended inputs are completely separate (and different) animals from the LFE input. First of all, ALL the controls on the back of the sub are operable when using the L+R inputs: phase, frequency crossover point and slopes, volume, high pass points (if you are sending the signal on to your main speakers) certain room-correction circuitry if your sub has room correction features (such as a microphone to set them up.) The subwoofer's amplifier only 'samples' the low frequency content of the L+R signals anyway (meaning, the actual L+R signals coming from your preamp/processor dont really 'drive' the subwoofer amp directly, whereas the LFE signal DOES actually drive the subwoofer amp.) So by keeping the L+R signals (coming from your preamp/processor) separate, you don't run the risk of compromising the output circuits of the preamp/processor by using a 'Y' connector. You can not (and should not) have signal going into BOTH the L+R inputs and the LFE input at the same time UNLESS there is a way at the sub or at the processor to turn one of them off as applicable.
All that said, the Woodmere II's already go down to 25Hz (at least according to the manufacturer ;~) so in your modest size room, with all those drivers going already, I can't imagine what you think you'll gain by adding a subwoofer?
