My recollection is that the maximum gain offered by the preamp stage of the DCC2 is either 8dB or 9dB. If you use the outputs from the DCC2 labeled "Analog Preamp Output" that are controlled by the DCC2's volume control, you are running the signal through the analog preamp stage. A volume of 99 would apply the full gain available from the DCC2's preamp.
It just occurred to me, though, that there are two additional sets of outputs (one RCA, one XLR) on the DCC2 labeled "Analog Line Output" that, I believe, bypass the analog preamp. I suspect you can use those outputs to achieve unity gain for the signal from your home theatre processor. I believe the output signal from these outputs is at a fixed level not at all affected by the DCC2's volume control, so the volume setting should be irrelevant.
It just occurred to me, though, that there are two additional sets of outputs (one RCA, one XLR) on the DCC2 labeled "Analog Line Output" that, I believe, bypass the analog preamp. I suspect you can use those outputs to achieve unity gain for the signal from your home theatre processor. I believe the output signal from these outputs is at a fixed level not at all affected by the DCC2's volume control, so the volume setting should be irrelevant.