In a 2 way OB the mid/high frequency driver is always full range and highly efficient in most cases. I drive mine with 2a3 SET tube amps making all of 3.5 watts. 90% of all music is played in the mid-range and that is the strength of full range drivers which produce mids to die for.

The bass OB woofers ( like the Sansui above ) I drive separately ( bi-amp ) with more powerful solid state amps. My Dayton mono-blocks make 150 wpc and the av receivers are around 100.

The older and cheaper non HDMI AV receivers are perfect for bi-amping the bass OB's as they will accept the digital signal from the CDP while the tube amp simultaneously drives the mids/highs with the CDP analog signal. High end solid state is not necessary for good bass in OB.

What you get from bass augmentors like the Sansui OB pictured here is bass weight. We obsess over plumbing the depths but extension is not near as important as weight. Bass weight is what gives music it's foundation and without it, music sounds thin and non involving.