[Howard Davis[_2_]]

A direct-coupled solid state amp, whether class D or AB, is best for driving
a subwoofer.

I avoid Behringer products because this company is notorious for copying the
designs of existing products, cheapening them, and selling them at a lower
price than the originals.

A tube amp for a subwoofer? FORGET ABOUT IT!
No practical tube-based amp has the necessary low frequency power bandwidth
to function down to 16Hz or lower as well as it does in the midrange and
high end.