Were there any distinct differences in the quality of the audio or in practical application?
I've experimented a bit with these mics, and I would rather have the sound of my mic and my chosen mic pre. This digital solutions take that out of the equation for me. Obviously it is all personal preference. I have also stuck with Schoeps CMC5 bodies because they don't use any surface mount electronics. The CMC 6's do. The CMC 6's are 1 db quieter, but I generally find the CMC5 bodies more pleasing. I also use a Cooper CS-104 as a front end to my Sound Devices, which is full of Jensen Transformers, so I'm on the opposite side of the spectrum.
I haven't tried it yet, but I've been very interested in going digital with my Schoeps mics. Sennheiser has also released digital bodies for their mkh8000 line. The practical problem with AES-42 mic bodies in the field is that you have to find a recorder that accepts AES 42 inputs and provides clocking. At this point the Sound Devices 788T is the only recorder to my knowledge (perhaps Nagra and other super-high end recorders) that does this. Otherwise you have to use a breakout box, like the DMI boxes built by Neumann. Too bulky for me and the 788T is out of my budget.
I have recorded for a year now in a studio with a digital Neumann Solution D (owned by my work) and it sounds very nice, and gives you extended frequency response and a ton of clean gain. Although with sound effects, sometimes it's overkill. I'm pretty happy with a decent analog mic when recording car hood impacts...
Is there such a thing as a digital amplifier? I'm pretty sure you're not asking the difference between solid-state and tube preamps, but I'm pretty sure you're asking about preamps... in fact you might even be asking about the amplifier circuit built into the mic itself?
Either way, I'm pretty sure the amplifier you're interested to know about happens before the signal is converted into digital, in order to create a good signal/noise ratio.
I'm happy to be wrong, but this question just doesn't make any sense to me.