McIntosh preamps

What kind of sound difference or improvement are you looking for?

Any Mac preamp will work nicely, it just depends on how much you want to spend and if you want tube or solid state. You may want to ask at the McIntosh forum at Audiokarma.org 

I have a C2700 and MC611s. Glorious sound. The C2700 warms things up a bit. There is something to say about MAC synergy amongst components. Another option is Audio Research preamps which I have heard plays well with McIntosh.

I once had a C39 with my MC352 and it was a good fit. But McIntosh is always improving so a newer pre might help. Are you considering tubes or wanting to stay solid state? If you are, and it sounds like you are, just using 2 channel there are a number a great pre amps to choose from. Also are you wanting new or used?
Another avenue to explore is cables, what are you using now? When I had my 39/352 combo I went thru a number of cables and wound up using Cardas, but you may have different experience with your speakers. I had Infinity Kappa 7’s then on to Revel F32’s. If you try cables get ahold of The Cable Company and try their lending library, John is great to work with there.

Good Luck

Theo

PS, as Jeffry mentioned Audio Research plays well with McIntosh. I have a MC402 now but have had 3 Audio Research pre’s and don’t plan to change.