I would run in parallel, that is + amp to + of tweeter in and woofer in and - amp to - tweeter in and woofer in. This leaves the other 2 channels for a sub or rear speaker.
You could also run one of the four channels to each speaker.
Either way you end up with about the same power to each speaker, depending on whether or not your amp doubles power into 2 ohms (or 4*6/6+4 ohms).
Some amps are not as stable into 2 ohms and most amps have more noise into 2 ohms. If the amp is stable into 2 ohms the noise should not be an issue. If the amp can't drive 2 ohms stereo I would buy another or run each channel to 1 speaker.
