The answer to that is that your speaker is not 6 ohms. No speaker is 4, 5, 6, 8, or 10 ohms. That number is the AVERAGE impedance of the speaker using a non-standardized test. Listen to the speaker both ways and enjoy the best way. You cannot damage anything.
4 ohm or 8 ohm tap
I have a pair of AZ Adagios, they are 6 ohm speakers. Should I use the 4 or 8 ohm taps on my tube monoblocks?