I've owned several pieces of McIntosh equipment over the years, currently have a C2500 paired with an MC452 to drive a pair of Focal speakers. I think the C2600 has an upgraded built in DAC compared to the C2500; in my case I used a PS Audio DirectStream DAC, so that difference didn't make sense to me.
After breaking the C2500 in I upgraded the tubes to Gold Lions and that further improved the sound quality.
After breaking the C2500 in I upgraded the tubes to Gold Lions and that further improved the sound quality.