Some would probably class this amp as neutral, but I actually find it a little laid back. I would class Bryston as a more neutral amp.
As for matching KEF Reference, which Reference are you referring to? Tonally, I'd say they'd suit the tighter MkI and the current MkII 200 series rather than the previous Coupled Cavity models, which are warmer sounding.
While it is powerful enough to drive the current Reference series, I wouldn't say that it is the most ideal amplifier for them. It is stable enough, but I don't feel it has enough bass control - I'm not saying it is lacking in this area, its just that the Reference range is dry demanding in this respect. I've heard plenty of high quality amplifiers that do a very good job driving them, but the bass just isn't as tight and dynamic as it should be.
Any amplifier can sound great, but it needs to be used with a suitable speaker. If both can work together within their comfortable limits, you should end up with a good sound that isn't seriously lacking in any areas.