People who favor the CMC 5 seem to do so on the basis that it is built with all-discrete components, and they have an ideological position which tells them that the integrated circuits in the CMC 6 (and CMC 1) can't possibly sound as good. Even people who should know better seem to be baffled by the small size of the components used in modern audio circuitry. In this case it is obvious that they are betraying their own notion of letting their ears decide, because they are instead pre-deciding what they hear on the basis of what they see. In actual listening comparisons, the size of the components doesn't matter (we're not talking about transformers, for example, where a certain amount of physical bulk may actually be required).
Of course such people will deny up and down that they are biased, but they are precisely the people who never submit to double-blind A/B testing, which can be such a great teacher of humility.
--The CMC 1 has one specification (besides the current requirement and the SPL limit) that is different from previous CMC amplifiers, and that is that its very low output impedance is strictly maintained throughout the audio frequency band. This could matter sonically if the input of the preamp or recorder has distinctly lower impedance than the specified 1 kOhm minimum. There are a couple of preamps out there that have switchable input impedance, and others that dip below 1 kOhm at one or both ends of the spectrum while being up to spec in the middle. Such preamps can interact audibly with any microphone whose output impedance rises at one end or the other (Ohm's Law).
As an example, ribbon microphones generally have higher output impedance at and around their primary resonance frequency; that impedance can even exceed 1 kOhm. This is why the best preamps for ribbon microphones, such as AEA's, have high input impedance (20 kOhms or even higher) across the frequency spectrum. Otherwise, the microphone will sound rather different depending on which preamp it is connected to. You aren't hearing the mike's own response, but its response as filtered through frequency-specific losses (possibly of several dB) in the input impedance of the preamp. In an extreme case--say, a preamp set for only 200 Ohms input impedance--the frequency response of the CMC 1 would be flatter than that of any previous CMC amplifier to a potentially audible degree, because its interface losses would be uniform across the spectrum, while those of the older amplifiers would be greater at the frequency extremes.
(It's still Really Bad Engineering to design or use such a preamp in my opinion--but to some people everything is a "tone control", and they want more "tone controls" no matter how they're obtained.)
--best regards