Yes, things should either be matched by price or performance. Price/Gain-wise bookshelves would always win. Performance-wise, at a certain point I guess towers+sub/subs would take over and bookshelves+sub/subs wouldn't catch up any more. Going even further, at a certain price point you might not NEED a sub, but could always profit from one (maybe not with Legacy Audio Valor).
Also, as
@yepimonfire said; fair comparison would have drivers matched in both towers and bookshelves.
There's another thing that's buggin' me. I'll use adjectives and nonprofessional terms, so I apologize up front. There's the
size of the sound. As
@MrBoat said perfectly; there's no replacement for displacement.
Going through many dedicated listening rooms that are no bigger/smaller than mine, I've noticed that not only the quality of sound played a role. Speakers with large drivers gave a feeling of large sound (or am I being biased?) Going by how easily I could converse with others who auditioned the gear (and only by that), I'd say it wasn't the SPL. I can further confirm this with another (completely unreliable) proof; no matter how much I turn the volume up on my speakers, I don't get the size. I get the SPL, but not the size. You can get accuracy and still miss this feeling of a large sound stage.
This is not only woofers, but, even more,
midds! You need big, powerful and well handled midds and lower midds. Just the other day I've watched a video that features at the moment on home page of this site (well not anymore, but it's the one about
Audio Legacy Valor speakers) and I heard
@gene saying the same thing; (paraphrase) having small/smallish mains and adding an army of subs is not getting you there.
I remember asking about this in my
Floorstanders vs. Bookshelves - a different approach thread, where I wanted to talk about all the differences other than sufficient bass and the size of the room.
My conclusion is that there really is no replacement. Even if you're in a small room, small speakers will not start to sound "large". I'm not even fully convinced that small rooms don't need a sub - what type/size of a wall would you need to have, to get reinforcement bellow 40Hz? I think that a more serious problem would be whether sound waves bellow 60Hz would have enough space to develop in a small room. But in this case I feel it would be fair to say; you're gonna miss it, but small rooms are not good for sound reproduction.
What I'm interested in now, is how much would you miss the woofer in a large mid or mid/woofer bookshelf and a sub or subs combo? Something like Dynaudio Special40 with 170mm mid/woofer driver, or Revel Concerta2 M-16 & B&W 805 d3 with 165.10mm mid/woofer. Would you, in this case, have an easier or harder job of integration and would it be good enough for the feeling of a large size sound?