Hi. I own that precise "combo" (Luxman L-590AXII + Kef R11) and these two, get along very well. I tried to home demo several different combinations (Pass Labs, Rega top level models, other Luxman models - as the mentioned L-509 etc.) and this Class A integrated amp is all that I apreciate more for my taste.
Even the L-509 (Luxman) didn´t match so well with these R11 speakers. I know very well the most of the Luxman models (that I love) and they depend a lot of the speakers match. Even the new (and limited edition) L-595 didn´t match the R11 as great as the L590AXII. Its a excellent amp (class A too, a little bit more smooth in the highs maybe, but in the lower parts I did like more the L-590AXII).
I am quite satisfied in all frequencies. The bass is powerful and with that full body sound feeling (not boomy but tight), the medle range is very sweet and unique on these class A amps, the higs very smooth.
As sources I use analog and digital, and in both ways are great.
Any question or doubt feel free to ask here or in private.
Cheers