If you are going to stay with the speakers, I would opt for which amp outputs the most current at the 4-ohm ratings. I don’t know if they dip much below that at lower frequencies. I had the 509Z and absolutely loved the amp. Luxman rates the 507Z at 210wpc at 4 ohms. Even though they are outstanding amps, over time I do not know how well it will stand up to the 4-ohm spec. Contact Luxman and ask what they think. If they say it’s fine then I can promise you will not be disappointed with the 507Z.
edit: or go with the Hegel H390 or H590 and never worry about that potential issue again.