My use case is mostly from a 2-channel perspective and a small(ish) listening space.
With the KEF R300 (older R series) I have used/heard the following amps:
Marantz PM7001 (Integrated Amp 70/100Wpc)
Marantz NR1605 (AVR 50Wpc)
Onkyo TX-DS595 (AVR 75Wpc)
Outlaw Audio M2200 (Poweramp 200/300Wpc)
Parasound NC275v2 (Poweramp 90/150Wpc)
AKSA v2.1 (Poweramp 55Wpc)
Pass F7 (Poweramp 20Wpc)
Except the Pass amp, I own the rest of them, so my observations are over a period of time, not short audition.
In terms of drive capability, the AVRs used to struggle a bit at higher volumes.
Marantz PM7001 in IA mode does a good job, but heats up after an hour or so (but it does so even in preamp mode, no speakers connected)
Outlaws are pure muscle no finesse; great for HT, do not even get warm.
AKSA is the sweetest sounding for music sessions. Never tried it in HT scenario.
Pass F7 is a classA amp that also sounded as good as the AKSA above.
Parasound is neutral in terms of presentation. No issues driving the speakers.
I got the Parasound to power the main speakers (KEFs and L/R) and use it in both 2-ch and HT scenarios.
The sound signature/quality can best be described as clean and effortless.
I have moved this amp to power smaller cubes since I have a split chain now. One for HT one for 2-ch.
My guess is you'll get similar performance with 5250 vis-a-vis 275v2.
A52 may be a bit more nuanced or refined for "critical" music listening.
If your usage is mainly HT, these nuances don't really matter. And there will be a sub in the mix.
BTW, KEF R3 is not a power hungry speaker. It can work with a wide variety of amps.
They do come alive and excel when they have a bit of "authority" behind them.
A SS amp that holds its ground up to the first 50W is a decent pair up. Anything more is headroom.
I have to admit I used to chase after "watts" until AKSA (55Wpc) and 275v2 (90Wpc) humbled me to change my opinion

My rig has a sub (REL T9/i) for both 2-channel and HT usage.
Cheers,
Raghu