Actually I suspect that PLIIx would still work well for Dolby EX tracks too, since all EX is doing is matrixing the back channel into the surrounds. Be aware, though, that some EX-encoded discs will use a more aggressive form of the EX flag that will force the 990 (or any other properly-programmed Dolby Digital processor) to use EX whether you asked for PLIIx or not. Case on point: I have found that the Lord of the Rings EE discs use the more aggressive EX flag, so the 990 will use EX (and changing it manually will be overridden if the 990 is forced to re-acquire the signal because I changed inputs or went into the DVD menu and returned to the program), but the Revenge of the Sith disc is EX encoded without using the flag (so the 990 automatically treats it as a Dolby Digital track and applies PLIIx for me).