What I can say is that if you got an outstanding preamp or intend to drive a power amp directly from the DAC, then the new one would be the ideal candidate. If you need USB performance, or a headphone amp that can match an equivalent £200 headphone amp in its own right, then again the new unit would be up your street. But if none of the above applies to you, then the TC-7510 is more than adequate.
The biggest problem I found was that many preamps are inferior sounding as a preamp when compared to the new DAC. So running the DAC through a half decent preamp is not going to offer you much improvements. It is hard to explain properly, without physically trying out what I just described. It's one of those things that makes people say it is impossible, until you hear it for yourself.