Actually yes, this is something I should have went into. And NomoSony is correct. If you are using a Dolby Digital DVD then all speakers should light up.
Granted as I said its a DD 5.1 dvd, and we know you are using a optical cable, so we know its a digital signal. What model dvd player are you using?
With mine, when using a 2.0 DVD it will go into ProLogic 2x mode, and the only lights that will light up are the L&R&S (Left/Right/Sub) However the ProL2x will put sound out to the surrounds and the center.
But in your case only the L/R lights would come on, for a 2.0 dvd.
Thats why I had assumed you have at least 1 movie on dvd thats DD 5.1
Granted, I still say the only way to use the receivers processing is to directly connect the speakers to the receiver. And setting them to large/small will make no difference if you have them hooked through the Bose sub.