Looking for power amp with warm, smooth sound

Cayin A-50T - tubes and wonderful. $1,200 new should be doable.

I have one into B&W 685's and it sounds sweet. Very sweet.

The RS6's are a pretty bright speaker. I may consider trying to sell them and use the money you set aside for an amp towards a speaker upgrade.

Second the Cayin A-50T...excellent amp! Sonics, cosmetics, build - all first rate!!!

BAT VK200
ODYSSEY STRATOS SE
ROTEL 1080

Any of these should do it.

If not... and even before throwing another amp at things, maybe adding a power filter for a couple hundred might help, like the UPC 200 from PS Audio.

If the receiver has a migratory power cord, that option too should be explored.

I overlooked cabling and conditioning early on and went through a lot more $$$ than I might have, had I looked into those accessories as a solution. Instead I began replacing components and that's an expensive lesson as ultimately they needed to be addressed.

Good luck.

Do not go with the Rotel 1080 if you are looking to warm up those speakers. Ii have owned the 1080 and it is anything but WARM, it is certainly on the bright side. The Cayin would be a good choice as would a Jolida 302BRC. The Jolida is an integrated using EL-34 tubes thus giving you the ability to take the reciever out of the mix if you wish.