What is the best loudspeaker for a small room?

One advice is a small speaker and a subwoofer. Because this you can adjust very easily. I did this many times for small rooms. Gives better results then 1 pair of speakers. I had the 100.5 and XP20 as well. I would choose for a speaker which can give a very 3d holographic sound. The Pl-200 of Monitor Audio is in his pricetag by far the most hlographic speaker I know to date. You can put it very near the wall. It is developed for this. I never heard a speaker what so easilly good at even small rooms are rooms with a bad acoustic. Read the Stereophile test of the Pl200. Other thing is you can use a Onkyo PR-SC5509 with Audessey pro. Know my stagte is deeper and wider then with the XP-20. Detalis are better focussed wenn I had the Xp-20. Audessey pro brings you to a very high level of music without all the flaws of a room without loosing drive and details. I never thought I would like this more over my XP-20 which I had before.

I owned the XP-20 and XA100.5 as well. This set is a very musical and powerful combination. And can play very 3d holographic. The biggest fault you can make is buying a speaker which is not capable of a deep and wide stage. Like B&W. Which most expensice ones I owned. How much money you would want to spend? Many speakers need some room from the wall. Kef, avalon, dynaudioand B&W are all difficult to use in a small room.

The kef you are using is not that special. I sold them, but I would not want them even for free in my room. Your system can reach a much higher level with other speakers. Filters of kef speakers are not the best. In 3d imaging kef is not even of the level of many other good speakers can. Bass respons is not fast enough.