Affordable is questionable for what you are getting.... Im not sure I want a 9 inch panel and twin 8's for $6500 plus.. I do like the theory of going back to passive subs as I like to control my speakers
give me twin 8 or a 10 and 8 as well as a 12 inch 48 inch panel "A LA" Odyssey and now your talking.. Not that I am partial as I am a Odyssey owner and like the design really well.. Better than my CLS !
Really more of an in-between replacement above the Theos and below the Ethos. About the same spec as the Ethos, but you have to Supply your own LF power. Which I would actually somewhat prefer, although I think the "secret sauce" for integrating the panel to the woofer comes from the DSP. If I were going to design a special speaker something like the Expression with no powered bass, but outboard electronic crossover with either DSP or active analog would be the way to go. With analog electronic crossover between the pre and power amp you could use high tolerance R and C components and no inductors at all. You can add in gain at certain frequencies if required to extend LF response and or mate with the panel.
I have a pair of Classic ESL-9's for three weeks now in my 16 X 26 foot (8' ceiling) dedicated listening room. The integration of the bass is fabulous on these speakers in my room. I am truly impressed so far.