Yes, the unit is decoding and playing a Dolby TrueHD signal when the display reads “Dolby HD +XS”, etc.  Many of the HD soundtracks available today are recorded in 5.1, not 7.1.  However, if you have a 7.1 audio system you likely will want all 7 speakers (and subwoofer) playing when you listen to a Blu-Ray disc.  When this is the case, the Rotel processor can apply additional processing to the 5.1 HD signal to matrix out additional channels for the 6th & 7th channels in the system.  You have a choice of 3 or 4 distinct methods to do this:
Dolby Digital EX (Available for Dolby 5.1 modes only)

Dolby Pro Logic IIx Music

Dolby Pro Logic IIx Cinema

Rotel XS (Extended Surround)
Using these additional processing modes does not compromise the original HD content for the 5.1 channels; it simply allows you to add the extra back channels when playing these 5.1 soundtracks.

For more detailed information on these different modes, refer to the owner’s manual for your product.