I owned 184's and listened to 42's and really REALLY liked what I heard. I agree with people that say they sound quite alot alike. That said, I also had a SD MP-2 and I can say for my own personal tastes that I thought the 184 and MP-2 were a pretty poor match...but that's just me.
Here's my reasoning...the wonderful thing about the 184's and I think also the C-42's is how clean and clear the bass rings through. I feel like I can actually hear the string vibrate on the recordings I made with the 184's. My experience with my MP-2 was that the MP-2 took AWAY detail in that same frequency range and kinda muddied those frequencies up. So, to my ears, the MP-2 negates the very essense of what makes the 184's and C-42's such great sounding mics.
In my experience, MP-2 users like the pre-amp for the fact that it is a 'go-to' preamp for warming up the sound and I agree with that, but I think you sacrifice low end detail in the process and that is NOT something I was happy with in my setup. Besides, warmth is not really something that these mics need. So, I'd personally DEF leave the MP-2 home in favor of something that will give you a clean transparent low end.
Having said all of this, I do want to say again that this was all based on my conclusions from running 184's...I've never owned the C-42's.
So just another opinion.