What are you intending your Intermix Chamber's function to be?
Is it, to you, an earlier version of the TNG 'Warp Core'?
Or is it a very long raw power conduit with the reactants at the base?
Or is it a very long reactor, with matter/anti-matter slowly being introduced together through the whole unit, perhaps with dilithium being used in every segment?
I just think how you think it works to be the main thing to wrestle with before you design it - and if you've worked it out or have an opinion, I'd love to hear it! =)
Something old I had (and I'm not claiming this works well):
-TOS had a pretty large reactor, used little Dilithium, but depleted it at very high rates when under high loads. Dilithium is used (1)to mediate the reaction and (2) convert the energy into usable radiation.
-TOS had reactors in the nacelles which used dilithium as a mediator. Power was fed down and put into usable energy by other dilithium crystals.
-Intermix Shaft/Energizers - used LOTS of Dilithium but depleted it very slowly under all load levels. There's an initial reaction at the bottom of the shaft and more and more reactants are fed up, with dilithium in each transfer segment as well as being released as particles in the shaft to mediate and create the right kind of electrical charge. Some of the segments siphon off into power converting energizers. The whole thing was very complicated and very hard to manufacture - very costly in dilithium. The bigger/longer the Intermix shaft/Energizers, the more power the ship has.
--TNG (or...late movie) - reactor we're used to. Uses little crystal and it decays evenly, which is fine, because it can be recrystalized anyway (in TNG). Reaction is mediated by dilithium which causes plasma to energize. Step-down power is created somewhere other than main engineering.