The more channels you drive,the less power is typical.8 ohms is the standard for home theater receivers and systems.That is why a lot of them have a external or internal switch for 4 ohms.A lot of them put a 4 ohm resister in series in the 4 ohm setting.Wow, that really s**ks!!
The Maggies don't tell you when you split them if the highs are 8 ohms,and the lows are 8 ohms.They may be a little different than 8 ohms each half,but still look like they combine to 4 ohms.They wouldn't be 4 ohms each half,(that would make them 2 ohm speakers).I don't think that is true, and ElDartford's earlier comment about each section being 4 ohms is correct. Consider the non-biwired, non-biamped situation. At low frequencies, the speaker's crossover causes the high frequency section of the speaker to essentially not be seen by the amplifier (i.e., to be a very high impedance). At high frequencies, the speaker's crossover causes the low frequency section of the speaker to essentially not be seen by the amplifier (i.e., to be a very high impedance). So at any given frequency (apart from the crossover region) the amplifier sees the impedance of only one section of the speaker, not both sections in parallel.
Figure 1 of Stereophile's measurements of the MG1.6/QR shows its impedance characteristics. 4 ohms at low frequencies, 4 ohms at high frequencies, and a rise to over 18 ohms in the crossover region.
Regards,
-- Al