KEF Q Series vs. XQ Series?

Just wanted to know what the difference is between the two?
Thinking about picking up the Q900's to go with my Arcam. Is there a big difference in sq between them? Thanks for the help.
Yes, there is a big improvemnet to the X series. Better drivers, cabinets, and crossover parts. I've had XQ1 and Q1s and the sound moves from just ok to excellent.
I have KEF Q5s myself and wanted to upgrade to the XQ series so I went to audition them. What a disappointment. In the paper, the specifications look way better but at the end it's the sound what counts. The soundstage and depth on both are almost identical. The XQ is slightly more detailed in the highs but the midrange is not as enjoyable as in the Qs. Upper/mid bass is again the same on both. Lower bass is not a strength on either speaker, but you can easily tell the Qs go deeper into the 40Hz region and even some upper 30s, if well positioned.
KEF speakers need a musical amp to make them shine. Arcam is an excellent match for them. I have Marantz myself and they are a sweet combination for the price.