which Audio Research pre-amp?

@bdp24 is correct:  LISTEN to both in your system at home and then make a decision. What YOU like has no bearing on what others think or say or post.

As a former dealer, I am always amazed at people who do not wish to make their own decisions about gear.  Asking for opinions is an excellent way to weed out items that may have reps for breaking or poor manufacturer support, etc., and of course it is always nice to hear what others think about something subjective, but in reality, the decision is YOURS alone.

Take them both home and buy the one that sounds best to YOU.  As for cables, etc., well, let's just say that the electrons I have personally interviewed seem to be able to travel along wires fairly well regardless of the name on the box and let's leave it there.

Cheers, and good listening!

I have a Ref5se and had a VX-R then VX-R Twenty running first Vandersteen 5a the 7’s
pretty magical combo
i have heard the 6 in several very nice systems and gs as well but not isolated enough to understand subtlety between units.... good advice on getting them home if you can
the VX-R is a fantastic amp !!!
as for Ralph’s comments - consider his fine preamp also in your price range, when it comes time to replace my 5se, I will be doing that for sure
have fun !
enjoy your search and the music!!!!

For the life of me I cant figure out why your not going with an AYRE KX-R Twenty Pre instead of Arc.  I have the REF 10 and the KX-R Twenty so I am not biased (Fanboy) to either brand. Why would you think the synergy is better with Arc?

Get the ARC Ref 10 linestage if you can afford it. PSU is in a separate compartment unit. 
Quite a big step up from the Ref 6.
I had this Ref 10 linestage in my previous setup but I have since upgraded my setup and system to something else. 
But I'm still using the ARC 10 phonostage pre for my Kronos Pro turntable.

A reasonable question a-s, the answer being ARC pre-amps have a certain cache' amongst audiophiles. My question is, why doesn't the op audition both the ARC pre's he is interested in at an ARC dealer? Doesn't trust his own judgment, but "knows" that ARC pre's are "the best"?

I can't understand the cache'! There are better preamps out there for less money. But your point is well taken.