Производитель моего любимого усилителя, весьма мною ( и не только) уважаемый, не поленился написать в мануале буквально следующее -
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A Word About Impedance Matching
We strongly suggest that you experiment with the three available impedance connections for the best sonic match with your system. Since no loudspeaker represents an unchanging impedance at all frequencies, it is impossible to assert with certainty which output tap is appropriate to use. In many systems an amazing difference in sound will exist between the various impedance taps.
Since the impedance of most loudspeakers vary over a wide range experimentation is essential. We often find that matching a speaker's minimum impedance is more important than matching its nominal (average) impedance.
If you bi-wire your system (run separate speaker leads from the amplifier to the high and low frequency transducers) you may discover that two different impedance taps work best. For example, with early production Martin Logan Sequel II we find that the bass speaker is best matched with the 4 ohm tap, while the electrostatic panel is best controlled by the 2 ohm tap. On later production Sequels we use the 4 ohm connection to both drivers."

Думаю, для начала следует задаваться вопросом - каквой реальный импеданс колонок.....ну и стараться, чтобы "схема не свернулась"....