I have heard various Focal Arias, but they were on the end of Naim amps, which is a combination that I personally don't like...but sayng that, I think the "Focalness" of the Aria has been toned down a little from what they normally produce. I think they are more refined and a little less forward and "ruthless" sounding with amps of a similar nature.
Compared to the Kefs, I think they may be a touch cleaner and leaner, but for my taste, less smooth and less enjoyable.
The R300 have great scale for a standmount, but all that bass needs an amp with a vice like grip (which isn't cheap) and enough room to breathe. Only you can decide if the Elex provides enough control, though using the 2 part bung greatly helps to tame the bass.
I have heard good sounds coming from Elicit R with the R300s (Linn Majik DS as source).