With plate amps like the Adire ADA series, why go passive with tube amps? You have 2nd or 4th order low pass options (for sealed or ported monitors) and 2 bands of parametric EQ for each channel (if a stereo pair - which I recommend). Maximum flexibility to integrate with monitors, allowing them to roll off naturally on the low end. I use them and I'm most satisfied. My bass units are not subwoofers either - Focal 10W6452 10 inch woofers that contribute measurable output up to 200 Hz using 2nd order low pass with sealed monitors (Rat Shack analog meter). The monitor midrange/treble is startlingly clean using Atma-Sphere M60s, when freed from meaningful bass output (paired PHL 1240s in TMM). I gladly accept a measured 5dB dip between 100-125Hz as the price paid for otherwise flat in-room from 40Hz - 300Hz, as I don't notice it on music. I don't obscess over sub-35Hz for music anymore because there isn't much content that low and I'd rather not have to tame any more room modes than I already do. Going this route isn't for everyone, but eliminating a high pass crossover unit to the midbass drivers and sealing the monitor cabinets has audible benefits.
Any tube subwoofers out there?
I was just wondering out of the blue if there were any tube subwoofers, if not why not. Also are there any class A/B or other types beside the ubiquitous Class D? Just trying to learn more. Thanks