Not sure where you heard that ncores works best wit Tube pre.
They work fine with MDAC pre and even better with a separate pre like the Khozmo passive pre.
If you want deep and properly defined bass, then you might spend your money better on new speakers before you get ncores.
Ncores helped in my system but ultimately it was the speakers that made the biggest change.
Well, I read it here several times.. Users reported good experience with either source tube output stage or some form of tube pre.
And yes, I plan to firstly built Ncores and than find a good match with speakers.. I just wish I had larger room and could treat it .