I owned some KE F Q-series speakers. I have listened to the majority of the Q line and owned a 6.1 setup made of KEF Q series speakers for 2-3 years. I sold the set but still have a pair of KEF Q1 (bookshelves) speakers in my main sitting room, small and sound good.
I am not familiar with the XQ series, so what I will say reflects on the Q series only.
In my experience, the Q-series has GREAT mid-range, good high, and good low. I was content for a while with the KEFs but something kept nagging me that there is something missing from the sound. At the end I took a risk and ordered the Axiom 7.1 set. All the Axiom speakers are much better than the equivalent KEF speaker. This includes, clarity, headroom, and is specially clear when comparing the High of the speakers. I solf my KEFs immediatly afterwards and never looked back.
To my ears, the KEF's ate a little bit at the upper range and sacrificed some overall clarity. Axioms were much better. I have read that the Axiom range is mainly made of neutral speakers. I cannot vouch for that subjective statement, but the Axiom speakers were more detailed than the KEFs. The Axioms replaces the KEFS in a marble floored room. The room had bare walls, a sofa, and a small rug. The KEFs played fine in the room for a long time, however, when the Axioms came, the room suddenly sounded bright, probably because the KEFs mellowed upper range negated that effect. I added a slightly bigger rug to and that issue was resolved. In my opinion an investment worth making.
M80s compared to the upper range floor standing KEF Q sounds more detailed, and sound limitless. I have played the M80s to ear splitting volume, and they show no signs of reaching their limits. I have no idea how loud these monsters go, but I do not want to find out anytime soon. The KEFs show signs of strain at very high volumes.
Last thing is about efficiency. The Axioms played louder using the same equipment than the KEFs. This tells me that they are more efficeint speakers.
This is a summary of my experiences with the Q series of KEF. I am not sure that this will be useful, since you seem to be asking about a different series.
I am going on a short holiday and will not be accessing the forums during my leave.
All the best.
