4 or 8 ohm connection for a 6 ohm speaker?

Hi Bill, I would suggest the 4 ohm. Please report back your findings the differences.

It makes sense to try the lower tap first, but there definitely have been cases of particular combinations of amp and speaker where the tap a little over the nominal impedance sounds better.  Of course, if you ever look at some measurements, nominal impedance can be a pretty fuzzy term.

Roger Modjeski ( music reference ) advocates light loading but also listening. Clipping is bad, so listen for that also. I light load my Vandersteen TreoCT ( an engineered easy load at 6 ohm nominal ) with the 2 ohm tap on my RM-9. Amp stays in class A longer and at the relatively low volume I listen at - sounds better.
have fun - enjoy those great speakers! And the music !

As most have said already, try the lower option first. I have a pair of speakers that average around 12 ohms during play. I tried the 8 ohm posts first and was disappointed. I the 4 ohm post and the speakers sounded much better. 

HI, 
Some tube amps behave better on 8ohm taps. As your speakers demand a little push the 4ohm tap would propably be better but you wouldn't know till you have tried.