I have a mac C2700 tube preamp with the DAC2 board and its quite good, but a Chord Dave showed where its laking as it should for the money. The Chord Qutest gives you a good chunck of the Daves sound so i'm betting its a sound sig thing at this piont between the qutest and DAC2. Either is fine but eventualy your going to want to upgrade from either.
The DAC2 board is quite good as you mentioned but a $2500 DAC will be an upgrade in most cases. Mind you the DAC2 board gives you way more flexability, and easy TV integration if thats a needed thing.
I would not run two preamps if you want tube sound to try, get a tube buffer and stick it in between the pream and power amp.
Or sell the C53 and get a C2600/2700/2800 etc.