The Luxman 550AX is a very nice choice. If you find one used, I would be all over it. If that’s the kind of sound you’re after, your list should also include LTA ZOTL Ultralinear and LTA Z40 Integrated. Pass Labs INT-25 would also be a great choice, although a bit neutral and dry when directly compared to the LTA offerings.
However, I would not consider the PS Audio Strata unless you audition first. It is not in the same ballpark as the other amps mentioned in this thread. I have a strong aversion to dry sounding amps, that’s just my personal preference.