I've enjoyed a C2500 now for two years, swapped out the stock tubes for Gold Lions, immediately noticed a difference, especially in the midrange. I don't use the internal DAC. I suspect the main sonic difference between the C2500 & C2600 would be the performance of the built in DAC, which I suspect is improved in the C2600.
C2600 recommendations
What’s your thoughts on the McIntosh c2600 preamp compared to other McIntosh tube or SS preamps?