Most professional mastering engineers want to receive your material in the highest possible resolution, and many of them now have a MasterLink or a digital workstation that can read CD24 disks directly. If they're using analog processing, send your material as 24-bit, 96 kHz files. If they're using digital processing, they'd prefer 24/88.2 files (because then there will be a simpler sample-rate conversion to make a 44.1 kHz CD). For a complete album, you'll send several discs, since at these high rates a blank CD holds no more than 19 to 21 minutes of audio. To show the mastering engineer how you want to assemble the CD master, send written notes and a Red Book version of the CD sequenced the way you envision it.