One more thing on ohms the lower you can get the ohms without going below what the amp is rated the better sound and drive you will get out of your amp.
You're about half right and half dangerous.
A given amp will deliver more power, but it will NOT necessarily provide better sound when driving a lower impedance. The formula for power is:
P = E²/R
Power = the square of the voltage divided by resistance. That means, when the impedance is divided by two, an amplifier providing a given output voltage will be delivering four times the power into the load... IF the power ratings of the devices and the heatsinks are adequate to handle that much power.
As you note, connecting two similar speakers in parallel will present a load of 1/2 of the nominal impedance of one of the speakers. So yes, you'll get more power, but that doesn't say anything about the distortion of the system. Lowering the load impedance lowers the damping ratio, which is the ratio between the load and the electrical source impedance of the amplifier, itself. Typically, a higher the damping ratio (higher speaker impedance) results in lower distortion.
Furthermore, most amplifiers exhibit higher distortion with greater output power due to thermal and other physical characteristics of the output devices.
Then, there's the matter that the impedance of a speaker is not a linear resistance across its range of operation. At any given frequency, it is a complex value determined by the inductance and capacitance of the speaker coil, the natural resonant frequency of the mechanical speaker mechanism, the acoustical properties of the speaker enclosure and a number of other factors in addition to the DC resistance of the coil.
We haven't even touched the far more complex math of dealing with switching amplifiers (class D, class H, etc.), rather than linear amps, and though it's not germain to the OP's question, the game changes again when dealing with transformer coupled amplifiers, such as tube amps, where the amp and transformer are designed to operate over a much narrower range of loads.
The actual resistance of a speaker that is nominally rated at 8 ohms can vary from well below to tens of ohms greater than its rated impedance. This graph shows the impedance curves of three dynamic speakers.
Quoting from the source:
... the loudspeaker with the red trace had a low impedance of below 5 ohms at about 70Hz and at 25Hz the impedance was close to 50 ohms! The green trace is a different loudspeaker with the low impedance being about 7 ohms at 350Hz. and at the resonant point of 60Hz has an impedance of 40 ohms.
I cant stress enough about never dropping below the amps ohm rating it might work for a day it might work for a year but you will blow the finals in your amp sooner or later. so its best to stay above the ohm rating on any amp
You're right about not loading an amp beyond the manufacturer's specs because exceeding those ratings can be destructive to the amplifiers, but you're wrong to advise anyone that, without considering a lot of other factors, simply driving a lower impedance will result in "better" sound.