McIntosh D100 as Preamp

I only have digital sources so would there be any benefit to run D100 as a DAC through a C2300 amp or run the D100 straight to the power amplifier?
Not sure what you're trying to accomplish here.  Running a D100 into a C2300 pre is running two preamplifiers in series.  Are you outputting PCM (e.g. 24 bit 192 kHz or DSD) from your digital sources into some kind of a DAC now or are you using the analog outputs from your sources directly into your amp?

If you're trying to get a DAC with a tube output section into your power amp, a better choice would be a C2500 or C2600.  They both have internal DACs.  Fill us in and we can help you more effectively.