Logic Pro X surround bounces are not encoded. Surround bounce files can be encoded in the Compressor application, available in the Mac App Store, or with dedicated hardware devices and other software.
Common surround encoded formats include:
Dolby Digital: Dolby Digital (also known as AC3) includes the LFE channel. It is a compressed format, commonly used for DVDs and digital terrestrial or satellite TV broadcasts. It is also widely used for computer game soundtracks.
Dolby Digital True HD: An uncompressed (or minimally compressed) high bit-rate format, commonly used for Blu-ray discs and high definition digital terrestrial or satellite TV broadcasts.
SACD: Super Audio Compact Disc: The Sony-Philips version of DVD-A. SACD audio is stored in a format called Direct Stream Digital, which has a sampling rate of 2.8224 MHz. SACD discs must contain a stereo mix, but usually also offer a 5.1 mix (although this is optional).
Pro Logic II: Pro Logic II uses two full-range rear channels, unlike the original Pro Logic (LCRS) format. It does not, however, use the LFE channel. In other words, this is a 5.0 format, so simply disable the LFE channel in Logic Pro X if you want to deliver a Pro Logic II soundtrack.
DTS (Digital Theater Systems): Soundtracks generally sound better than Dolby Digital EX equivalents because they use a 3:1 compression ratio, whereas Dolby uses a 12:1 ratio. Less compression means more storage space is required on the delivery medium.
DTS HD Master Audio: An uncompressed (or minimally compressed) high bit-rate format, commonly used for Blu-ray discs and high definition digital terrestrial or satellite TV broadcasts.