I agree 100%. In fact, Yamaha NS-10's are a good example of a good (by many peoples opinion) monitor that really needs a sub complimenting them when working with today's music. Back in there day (pre subwoofers) there really was no need to augment them with a sub. But, today's home music systems, be it 2.1, 5.1, 7.1 or whatever, NS-10's will leave that whole sub region open to "whatever" and that same "whatever" will be reproduced in the home music system..
Again, I'm not disagreeing with the point(s) made here, just continuing the discussion. And I'm doing that by suggesting that if you're mixing for a 5.1+ system, that NS-10s (and similar) are - to put it softly - probably not the way to go for the mains.
Most (not all) modern x.1 home entertainment systems are not going to be using anything like the character of an NS-10 for the side channels. The center channel can sometimes be on the cheap on frequency response and may bump the mids to enhance dialog, but the other four or six will tend to avoid the high-mid bump of an NS-10, if for no other reason (though there ARE other good reasons) than to be able to stamp the THX certification on the box.
And speaking of THX, their standard spec is to crossover to the sub at 80Hz, and many movie soundtracks keep that in mind, not to mention the playback system design itself. Many home reckers use this as gospel and automatically set their crossovers that way. That's ideal if you are mixing for 5.1+ - assuming your sub and monitors are spec'd optimally for an 80Hz crossover. Now, some are, but I'm of the school, that one should not assume that, because that is not always in fact going to be the optimal crossover for any given main/sub marriage.
But if you're not necessarily mixing specifically for a 5.1+ multimedia playback, and your monitors are better crossed at, just for example, 55-60Hz, then I'd want the lower crossover. there can be a lot of stuff between 60 and 100Hz that can be coming from panned locations, and personally I wouldn't want those effectively automatically summed to mono, especially when it comes to mixes mastered in old-fashioned stereo

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Just all stuff that does come up with the question of using subs in the mix studio. It's up to the individual, of course, as to how deep they want to dive into the detail. But it never hurts to be well-armed informationally when going into these things.
IMHO, YMMV, NaCl, H
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G.