I've just been listening to the Seventh Veil loudspeaker system with Tom Evans' Soul (tube) Power amplifiers.
Initially the Soul amps were just used for the full-range speakers and an inexpensive solid-state power amps were used for the bass.
Changing to Soul amps for the subs as well as the mains made a dramatic difference top the bass, integration, tone and timing.
Of course the Soul amps have a far better bass end than many tube amplifiers and the solid-state amps used were relatively cheap and could, no doubt be easily surpassed.
Still, this listening session changed my ideas about amplifying subs (particularly with the Seventh Veil speakers). Ideally I would now go fo tube amps throughout, with the sub amps matching the main amps if possible.
Steve