Steve, as John said, the possible problem would be that the 4 ohm speaker would draw more current from the amplifier, the amp might start to overheat, and then its protective circuit would shut it off. Getting a little fancy, Ohm' Law states that current equals voltage divided by resistance(I=E/R), so if the voltage stayed the same but the resistance was 4 ohms instead of 8 ohms, theoretically twice as much current would flow, possibly creating an overheating problem. So, the lower impedance switch or setting reduces the maximum voltage(E)so that the lower R doesn't result in as much increased current(I). My suggestion would be to not make any assumptions about the adequacy of your 1400, which is a quite powerful receiver. Keep in mind that speakers of the sort that you'll be using draw about 1 watt at a comfortably loud average listening level. Split-second peaks might draw up to 100 watts or more, depending on several factors. See how things work out before you assume that you need more power.
