ARC Ref 6 VS. Vac Renaissance MK V

Vac is a better sounding preamp more neutral and more musical.Vac also has great service as well.

I have not heard either of your two choices but I do own the Renaissance mk1 which replaced an Audio Research preamp.  The build quality of the VAC is superior to the AR if that matters to you.  I would take the VAC without thinking twice.
The only limitation I noticed on the mk5 is only 3 inputs plus the phono, so if you have a lot of things to connect you have a problem.

I have the Ref 6; it was indeed a bit too forward and lean in bass when paired with a Rogue Ares Magnum phono stage. But recently I paired it with the VAC Renaissance stand-alone phono stage and WOW! That combination blows me away. At this level of gear, matching is crucial. Soon I’ll borrow my dealer’s Renaissance V line stage (when my new SE phono comes in) and see which wins. But the control of the Ref 6 would be extremely difficult to give up for the crude motorized analog pot of the VAC. I absolutely adore the ARC’s digital volume and balance control, etc.

I also used to own the Renaissance III line stage some years ago, and my impression is that the Ref 6 is notably better. But the V is interesting with its use of 6922 and transformer coupled outputs.

the build quality of the Ref 6 is spectacular, btw.

Mulveling, in terms of sound on the Ref 6: how did it compare with the VAC equipment you’ve listened to? Particularly the line stage? Thanks for your input. 

Like I said, I think the Ref 6 is notably better than the Renaissance III. Though I didn't own them at the same time, I had a Rogue Hera II for reference against each. The Ref 6 is the most detailed and has the best clarity; exceptionally clean and clear sound. Fast and free of all grain. With the new VAC phono, it also displays better extension on both ends. Dead neutral tone. 

The Ren III a beautiful midrange (as all VAC does), good treble sparkle (maybe a bit editorialized) but perhaps a bit of bloom in the bass. Its built in phono stage, like the new stand-alone stage, is decidedly on the warm side, but man I love their phonos. A more romantic sound overall. 

The Hera II was more neutral than the Ren III, with better bass, but has a slight haze to it (like SS haze), maybe from the fact that it's too high gain for my 96dB speakers and noise/microphonics was ever present in that setting. This preamp matched best with the Rogue Ares phono, not surprisingly.