It depends on the speaker design. see:
http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php
If you are designing for tubes, keep the load easy (or 16 ohms) and you will do very well with no need to biamplify.
Its a huge myth that you need large transistor amps to 'control' the woofers! The truth is that if you design the woofer array for the job, even dual 18" woofers can be handled by a small tube amp quite easily.
http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php
If you are designing for tubes, keep the load easy (or 16 ohms) and you will do very well with no need to biamplify.
Its a huge myth that you need large transistor amps to 'control' the woofers! The truth is that if you design the woofer array for the job, even dual 18" woofers can be handled by a small tube amp quite easily.