Actually, for those speakers, I'd set all speakers to small - unless you can get down close to 20Hz (or at least below 30Hz) at the -3dB point, it's technically not a full range speaker. Keep in mind that the crossover matters if you have the speaker set to "small." I'd suggest setting all speakers small, with crossovers of 60Hz for the mains (although you could try 40Hz to see how the two compare), 60Hz for the center, and 80Hz for the surrounds.

During DVD playback, the 990 will automatically engage Dolby Digital or DTS as needed. In addition to that, you can use Pro Logic II to achieve 5.1 from discs that contain only a Dolby 2.0 soundtrack. In my 7.1 system, I use Pro Logic IIx to get 7.1 sound from any DVD or TV program I'm watching. Granted, for some sources there is very little surround activity to be had even with PLII/IIx, but by and large I've been very happy with Pro Logic IIx.