I wish I knew more, or had more experience to comment further. When I bought my L-590AX I read all the Luxman reviews I could find, which certainly weren’t a tremendous amount. Most reviewers liked the sound of the two class A amps over the others, and the 590 over the 550. I have zero regrets. Bass is super, and very well controlled, midrange and highs are awesome, great detail, but not bright or forward. Also, from one review that I can no longer find, these amps are really only class A up to the rated 30 watts, and then switched to A/B, and were putting out about 90 watts/channel into 8 ohms.
There is an L-550AII currently for sale here for $2000. This would be a 20W amp, which was later superceded by the L-550AX, then the L-550AXII. It looks nice. For me, I didn’t want to wonder "what if", so I went to the 590.
Good luck,
L.
You might find this worth reading.
http://nordaudio.pl/uploads/pdf/luxman/test/20141202-EN-l590ax.pdf
There is an L-550AII currently for sale here for $2000. This would be a 20W amp, which was later superceded by the L-550AX, then the L-550AXII. It looks nice. For me, I didn’t want to wonder "what if", so I went to the 590.
Good luck,
L.
You might find this worth reading.
http://nordaudio.pl/uploads/pdf/luxman/test/20141202-EN-l590ax.pdf