A Class-A amp that may sound truly special with your speakers is the Valvet A4 Mkll. They are monoblocks that are rated at 55Wpc and 90Wpc into 8 and 4 Ohms, respectively, but with large power supplies they punch well above their weight. And according to Stereophile measurements your Ref 5s are relatively amp friendly given forgiving phase angles 89dB sensitivity. At $7850 new the Valvets are not much above the upper end of your price range.
Another amp that flies under the radar but would likely make your KEFs sing is the Clayton Audio S100 that delivers 100Wpc of pure Class A power and has a convenient low bias switch so power consumption and heat are reduced when not using the amp for critical listening. At $8500 MSRP it's a bit above your price range (isn't that always the way?) but is a serious amp and at least worth a look. Personally I'd take Clayton over a Pass amp, but that's me.
Hope this is at least somewhat useful, and best of luck in your search.
Another amp that flies under the radar but would likely make your KEFs sing is the Clayton Audio S100 that delivers 100Wpc of pure Class A power and has a convenient low bias switch so power consumption and heat are reduced when not using the amp for critical listening. At $8500 MSRP it's a bit above your price range (isn't that always the way?) but is a serious amp and at least worth a look. Personally I'd take Clayton over a Pass amp, but that's me.
Hope this is at least somewhat useful, and best of luck in your search.