Not sure what you mean by "perform as a preamp fed directly to an integrated amp." An integrated amp contains a preamp, by definition.
Also, re "if serving solely as a dac fed into a cd player as transport," the cd player or transport feeds the dac, not vice versa.
Basically, a dac (digital-to-analog converter) takes as inputs the digital outputs of a cd transport, or of a cd player used as a transport, converts its digital inputs into analog outputs, which are then fed into a preamplifier or integrated amplifier (or possibly directly into a power amplifier, if the dac provides a volume control function and sufficient output amplitude).
The dac has to have digital inputs provided to it or it will not do anything. If when you referred to connecting both the dac outputs and the cd player outputs to the integrated amplifier you meant that the cd player's digital outputs would be connected to the dac inputs, and the cd player's analog outputs (as well as the dac's outputs) would both be connected to the integrated amplifier (on separate amp inputs), that would probably work. But the only reason for doing that would be to facilitate switching between the DAC1 and the cd player's internal dac, perhaps for comparison purposes.
The reason I say "probably work" is that it seems conceivable (though unlikely) that having the components connected that way (cd player digital outputs to dac; cd player analog outputs to amp; dac analog outputs to amp) might introduce some amount of hum, due to ground-loop effects.