I really should stay out of this, but...
What are your room dimensions? The speakers you have are small; that is its largest selling point. The driver I believe within each is 2.5 inches in size, IMO not large enough to be classified as LARGE. If you do so, the AVR is counting on the speaker to be able to handle the full signal being fed to it.
I believe I saw that these speakers can only handle to 250 Hz, with a +/- 10 db range. So raising the center channel levels may not do much here. The sub cuts off about 150 Hz, so there is a gap in coverage in the lower spoken areas that won't be filled in.
My advice if you're going to stick with these speakers:
1. Raise the center channel level, but since these speakers are rated "between 4 and 8 ohms", you may have issues with clipping if you go too high.
2. Place the "sub" near the TV, since in this system the sub performs the unexpected function of carrying some of the dialogue.
3. I don't know the reason for setting these speakers as large. It may be that the Acoustimass system wants everything to see the full signal. That may be needed for the whole thing to work. If it were any other speaker system, I would take the published specs about the frequency response range and set the crossover to the proper value, setting the speakers to small. Since Bose doesn't publish specs, this is a nether land.
If it were me, I'd return these and get conventional speakers for the same price that perform well in the room. But it is your money, so good luck.