Mcintosh MA6500 vs Marantz PM6006 for low volume listening (and loudness compensation)

Hello. My speakers are a pair of KEF R7 and they do sound wonderful to me. Currently I'm powering them with a Rega Brio (the latest model) amplifier and the sound is amazing, not only the sweet sound of the instruments but the outstanding imaging and soundstage. My question is: I mostly hear music in the night and have to do it at low volumes because I don't want to wake up my daughter in the next room. I tried the "loudness" knob on a Yamaha S701 and it was so bad that I returned the amplifier. I think I would do better with "just" a loudness button. After doing a lot of research I found out that the Mcintosh MA6500 amplifier does have a loudness button and it sells (used) at about $2,500-$3,000 and being that's very hard to find a NEW amplifier with a loudness button, I found the Marantz PM6006 which also has a loudness button.

The PM6006 offer much less amp power than the MA6500, but in SOUND QUALITY, at low volume and with the loudness button turned on, would the Mcintosh amp sound better than the Marantz one? Other than sound quality I also appreciate in an amp high SNR and low distortion measures. 

Thank you very much!!
If your open to other options IMO you are prime candidate for a really good headphone rig.There are amazing tube HA's for a few hundred dollars & world class headphones from about $300.00 to sky's the limit.Late night listening would never be the same.