KEF Reference 3 or Raidho X2?

That Marantz unit is excellent.  It will more than do the job.
Regarding the amp, this is a tough one.  I have never heard that amp.  I tried researching it and available data is limited so my POV is based strictly on spec’s and is worth exactly what you paid for it compared to your own experience or someone who actually knows the amp.

This a relatively low wattage class AB.  If you are in a larger space or listen at higher volume, I would be concerned about how much you are taxing this amp.  I would rather it be Class A where output is constant and then, running volume at 90% would be no big deal.  

Secondarily, I know nothing about the internal parts used and the quality of the amplification.  Price makes me wonder but I have heard awesome, modestly priced amps and others that are awful.  Quality of transformer and caps is key here.  

Because of my recent experience with the Canor AI 1.10, I have a very favorable opinion of EHX KT88s.  They do a careful match and they can be brilliant.  
In the end, only you can know if this amp is up to the task. 
This amp may work with the Raidho’s.  I would not use this for the KEF’s unless you are in a small space.  

KEFs are more neutral than the Raidho - KEF generally following the science of speaker design supported by Floyd Toole's (and Harman Kardon's) research, which is a neutral on axis sound with lightly sloping off axis frequency response so as not to end up to bright in a real room.

Raidho's have a self-admittedly distinctive departure from neutral - something like the BBC dip, engineered in for a more laid back spacious presentation.

I auditioned Raidho and though I found the ribbon/cone integration perhaps the best I've ever heard, I was just too aware of the departure from neutral.  Too many instruments and musical parts that I knew through other speakers (e.g. my Thiel 3.7s) to have presence and drive in the music, where made distant and softer on the Raidhos, loosing immediacy and drive.

The Raidho bass does slam surprisingly hard though.

I've been trying to DIY the sound of Raidhos for years. I've gottento 85%. If you can get the real thing, DO IT! Keep smiling1

Hello,
One more thing is the Kef Reference series bass ports can be slightly customizable. They have a long or short insert that lets you tune the bass of the speaker to your room. I have heard most people prefer the longer insert because it controls the bass better. In my demo it was the same outcome. Someone I know said he was trying to get the shorter insert to work by adding IsoAcoustic footers. He thought the bass was better but it needed the IsoAcoustic Gaia 2s to tame it a little. What I am getting at is you can customize the KEFs speakers bass. That’s huge. Also, off axis they are so good. Don’t think of the Reference 1s as bookshelf speakers. Think of them as short towers. Because when it comes to the sound that’s exactly what they are. Again, If you are near the Chicagoland area this store will let you demo them in your home. https://holmaudio.com/
I hope this helps. 

I purchased the Reference 3 from Audiotroy. He was kind enough to bring the 3 and the 1 to my house. It was no contest . 6 months later , still loving them.