These different compiler related issues are often solved with IFDEF's. If you see here:
https://code.google.com/p/nxpascal/s.../src/nxInc.inc
there is for now only definitions for which compilers support inlining (by removing function and parameter overhead it can increase math functions performance great deal, at slightly higher memory cost). There could also be a {$DEFINE OldPng} that would only be active on older Delphi compiler versions. But again, as i don't have a Delphi it is difficult to do something like that on my own. Do the png's work then with no reference unit in uses list? I don't know where the new Delphi finds the needed PNG class, and since what version it was available.

bass.pas or nxBass.pas? If it's bass.pas, then it should be reported to them, possibly with suggests on how to fix them.