Trying different output impedance taps with tube amps

My Antique Sound Lab Tulip 2A3 SET amp has 4, 8 and 16 ohm taps. I had been running the 8 ohm taps, and had a friend over to listen. He suggested the 4 ohm taps might be a better match for my speakers (Audio Note AN-Es). He was right, and it made a really nice improvement.

If you have multiple taps on your amp(s) and have never tried the other ones, or haven't for a while, it's worth a shot. Even if you are using the recommended or “right” ones for your speakers, you might be surprised.
I had the same experience.  In my case I was running a McIntosh solid state amp with the auto transformers.  I was using the 8 ohm taps for my GE Triton Reference speakers.  On a whim I tried the 4 ohm taps, and Holy smokes, what a huge diffference for the
Absolutely agreed you never know which tap will work best until you try them all. Nominal impedance is truly nominal and real world conditions are varied. Happy listening!
Kevin Hayes, of VAC fame, always recommends trying all output tap configurations just for this reason.

As Ralph Karsten (Atma-Sphere) and Roger Modjeski (Music Reference) will tell you, the lower the impedance tap on a tube amp, the lower the output impedance (higher damping factor) and distortion, generally speaking. Unfortunately, that comes with less power, except in the case of the unique Music Reference RM-200, which produces more power at lower impedances.

Modjeski recommends using the lowest impedance tap possible that provides the power required, as the lower impedance taps drive the output the tubes the least/softest (they will therefore last longer), and with the least distortion. Plus the lower output impedance is really a significant benefit, allowing the amp to produce the flattest frequency response it is capable of.

I'm in agreement with those who advocate trying all the available amplifier taps and listen.  Each circumstance will be different and it's difficult to generalize if higher or lower tap is superior.   My amplifier has 8 and 16 ohm taps and my speakers are 14 ohm nominal.  I've tried both taps and  the 16 ohm tap offers cleanly the  better sound quality. 
I believe that Ralph has pointed out in the past that using the higher ohm tap results in less distortion, increased bandwidth and better efficiency.  
Roger Modjeski is definitely  a proponent of the "light loading" approach. Honestly it depends on the particular amplifier and speaker involved. My SET amplifier has no NFB  and this probably explains the better sound quality with the higher 16 ohm tap.