KEF is certainly a bigger name, but Aperion gives you a totally free in-home audition. I mean you still have to put it on your credit card, but the shipping is free both ways and there is no re-stocking fees.
If you can do the same with KEF, then it's great. Otherwise, you're taking a bigger risk. Just the name KEF does not guarantee that it will sound good.
For one thing, the aperion 5T is 55Hz-20kHz +/-3dB and 45Hz-20khz +/-6dB.
The KEF just says 40Hz-40KHz without any tolerance, so it could very well be 80Hz-20kHz +/-3dB. Who knows? You might want to email KEF and ask for a more detail frequency response - on and off axis, +/-3dB, +/-6dB, etc.
Now, separates vs receivers.
Most people here will end up getting a separate amplifier anyway. It's inevitable.
So let's just save some time and money later due to upgraditis. Let's just cut to the chase and get the amp + pre-pro.
I think they will sound about the same in direct modes, but your speakers might need more power. I don't know what the MINIMUM impedance load of the KEF & Aperion speakers are. For all we know, they might be 3 ohms. If that's the case, you definitely want the separate amp + pre-pro.