mc275

I have an MCD550 and looking to get mc275.
MCD 550 has a very nice DAC.
Would I need a preamp or is it possible to connect mcd to mc directly?
I don't plan on using any other sources besides CD player, perhaps digital source at some point in the future.
What is a function of a preamplifier beside providing a DAC and volume control? (which mcd has).
Currently I have my MCD connected to MA6600 integrated, and the sound is is very pleasing to me. However, I would like to try tubes. I listen to mostly classical music at moderate to high levels, very dynamic, is this a good idea?

My questions:

1. Do I need a Preamp
2. Can I use mcd directly to mc275
3. What is the function of a preamp in the above scenario?
4. If adding a preamp is helpful, please explain how?
5. Which one would be better fit for mc275 c22 or c2500
6.. If I choose a preamp with a build it DAC, how would that improve/worsen sound from MCD dac?
7. If I get C22, would I need an additional DAC if I add a digital source to my system? or can I somehow run it through the MCD without sacrificing sound quality?
8. Is it a good idea for classical music