Audio research ref 6SE vs world

Makes perfect sense.  
It’s funny.  When I think of VAC, I was thinking of higher priced units.  I have a customer who has the VAC Master preamp and it is insanely good but is much more at $28K.  He was joking that he was going to have his coffin fitted with room for that preamp.  At least I think he was joking.  
VAC would be my first choice.  Completely forgot about it.  The Signature MKiia SE would be an incredible option.  A hair more than the ARC but incredible unit.  
At a lower price, possibly the McIntosh C70?  Not quite on the same league as VAC or ARC but a hell of a nice preamp.  

You might give Don Sachs a call.  He normally uses only one balanced In/Out pair but you can opt for more instead of RCA.  For a pure tube pre it is very quiet and clean sounding not syrupy and rolled off.  I purchased one just to play with and after a few months switching it in and out of my system sold both my ref-6SE and my PS-BHK to use only the Sachs which was a particularly good match to my system... that's the key, your mileage may vary.  It's only ~$3k loaded up.

I recently replaced my Aric audio unlimited line stage with a used Pass xp-10.  I noticed more detail, but the warmth didn't change.

Aesthetix, VTL, Herron - not better, just different at he altitude of the 6. I have a REF5se.

You might consider BAT preamps. Fully balanced and tube or SS options.