How important is a preamp for purely digital sources?


I’m currently deciding if I need a pre-amp in my setup.
I’ll be using a Bluesound Node 2i as the source and a McIntosh MC7100 as the power amp.

the question is ... how much sound improvement will I get by adding a pre-amp knowing that all my source material will be digital? Will it be more beneficial if I add a quality external DAC instead?

Thanks!!
dookie30
Enormously important!   However, there are not very many good preamplifiers on the market and the good one's are very expensive. 
@pinemountainclub: there are plenty of excellent preamps available on the used marketplace - ranging in price from $150 to $10K + !