From a perspective of someone who used to own a C2200 (used to!!!), I would keep the AR. The Mc sounded thin and lean to me, and the phono stage was very noisy. Just my $.02.
Well, I think you are talking about 2 different animals here. I currently own a Mac2102/C2200 combo and firstly can attest that the sound of the C2200 is any but thin and lean and is a big step up from the ARC SP9 (I used to own an ARC LS5mkIII line stage and Ref PH3). BUT, the phono stage in the C2200 can't compare to the ARC Reference Phono. If you listen to alot of vinyl, go with the ARC, you won't be happy with the MAC. Now if you do go with the ARC, do yourself a favor and later upgrade the SP9. To my ears the ARC LS5mkIII was better than the LS25mkI or II and at the prices you can grab these for, they are a steal. Good Luck!
Mc sounding thin and lean????? That is definately a first! I have auditioned ARC at length and currently own an LS3b and agree with Michaela that ARC is the one that is lean if anything. My McIntoshes are definately sweeter overall.
Stereophile and TAS both state in the recommended components lists that the Mc preamps are the quietest they have ever used.
But go with your ears and see what you think. Good luck! Arthur