Since your CDs are recorded at 44.1kHz, using 48kHz will not only not gain you anything, but the resampling needed will cause you to actually lose quality. So definitely stick with 44.1kHz.

(I think that empeg has to resample non-44.1kHz-sampled tracks back to 44.1kHz anyway, so it might always be better to go with 44.1kHz, even on sources that are not 44.1kHz, since you can conceivably control the resampling on your computer; I don't know how good the empeg's resampling technology is. I could also be wrong about this whole paragraph about the empeg needing to resample.)