I'm a bit confused by all of the specifications presented by vendors sometimes. For example, Arcam provides the following specifications:

8 Ohms, five channels 70W
8 Ohms, two channels 90W
8 Ohms, single channel 100W

However, they allow you to set the amplifier to either 4 ohms or 8 ohms depending on the speakers. When you set it to less ohms do you get more or less wattage? What are you supposed to set it to if your speakers say Nominal 6 Ohms, Minimum 4 Ohms. What is the difference between Nominal and minimum? If a speaker is rated from 10-150 Watts (Program 100 / Dynamic Peak 200), what size receiver do you need each channel to put out for a good match? Is 70 Watts enough, or is 100 Watts Better?