Theoretically a smaller driver with greater excursion can go deep but at the expense of sensitivity. Ports or transmission line can extend frequency response down as well. There's no substitute for a big driver in a big box, though. In my experience you can never get the same visceral impact from small speakers, with or without a sub, that you can get from big ones. If you're determined to try, the best way to go is active. Active bass is better. I consider an 8" driver to be the smallest driver that can begin to give a satisfying punch and go deep enough to not sound wimpy or low resolution on music with siginificant bass content.
Is there some reason you absolutely can't have floorstanders? Small floorstanders with a pair of 7 or 8" woofers will have a far better chance of satisfying you than another bookshelf speaker. If you've got your SIlverlines on stands the amount of floorspace taken up will be about the same.
Is there some reason you absolutely can't have floorstanders? Small floorstanders with a pair of 7 or 8" woofers will have a far better chance of satisfying you than another bookshelf speaker. If you've got your SIlverlines on stands the amount of floorspace taken up will be about the same.