DCL hasn't even worked out their flights and hotels to Barcelona yet. - But they will sell you airport to dock transportation.
As far as taking a train from Paris to Barcelona - that is a 12 hour trip if everything runs on time. Having done a couple of overnight trains in Europe when I was in my 20s, my suggestion is don't. Both times I barely slept and was a wreck the next day. Noise, motion, crowdedness all contributed to it. The compartments have 4 or 6 berths laterally placed - so as the car rocks side to side you are moving with it.
I also saw someplace people at Fodor's talking about personal security issues on overnight trains in Europe.