Kiza
I played the Class AB amp at 100 watts (505), the 20 watt N100 Neoclassico tube amp, and Class A 20 watt (I believe it was model 550). I did not preview the 590.
I auditioned a wide variety of speakers as well. These included ATC 11s and 19s, Harbeth 40.1, KEF 201s, Spendor A1 and A6s, Zu Essence, Devore 8s and 9s, and B & W 805s and 801s.
I thought the ATC and Harbeth sounded best with the 505.
100 watts easily drive both speakers. Really added nice mid range depth to vocals (the English BBC side to these speakers) which married well to my audio content (acoustic, punk, indie, reggae, funk).
I liked the Devores and Zus with the N100. The Devores threw a better soundstage in a small room environment, very neutral and "human", and the Zus had better dynamics in vocals, piano and cymbals. More lively, not hot. I have never been a fan of this company, Zu, but the new line is wonderful at 3,500/pair with tubes like Luxman.
Almost all the speakers listed above sounded great with the 550, except for power hungry ATCs were a tad understated and not fully formed. Spendors and B & W sounded fantastic.
Agree with your comments about the Luxman over the 6300, but to my ears, I thought the differences were narrow versus wide. The 6300 sounded great with speakers who relish solid state clarity. I thought they were very quiet with the sound emerging from blackness. The Luxman had an added lushness. It seemed you could hear more detail, but not in an analytical sort of way.