How do small woofers produce large bass?

So the 1723's are listed as dual 6.5", not dual 8". 

The answer is usually in the room and damping.  A modest room with good damping of the mid to high frequencies can sound much larger than you'd think, even with single 6.5" drivers.  

If you ask, can they go loud enough if high passed for a modest room? Sure.  Will they produce effortless sub-20 Hz? No. 

Of the speakers you mention, the Dali's are the most troublesome.  Some are tuned with a deliberate high frequency shelf, which can be great for low level detail listening but can also be too bright and tiring otherwise, so listen for extended periods of time and don't be fooled by "I can't believe I never heard this" kind of effects. 

If you want something fun, maybe try the Klipsch Heresy's.  That will be a night/day experience compared to what you are listening to now. :) 

Usually, they can't.  You could get more bass from a smaller driver by pushing it to a longer excursion limit.  But that usually takes a lot of power and/ or EQ'ing of the signal to get that deep bass.  This is how small subwoofers like the KEF offerings produce deep bass.  They have a big amplifier and a lot of EQ built into the control board of the sub.

Also, a smaller woofer, such as a 6.5" unit could produce a 20Hz tone....but maybe only at about 60dB, rather than 90dB+ like a 15" subwoofer driver could.  A headphone driver can produce a 20Hz tone that you can hear as long as you're wearing the headphones.  From a meter away?  No.  Not even close.

Most speakers today have smaller woofers due to design choices.  This keeps the cabinets narrow and not as wide as something like a Klipsch Forte.  So to compensate, multiple smaller drivers combine to try to add up to the piston area of 1 larger woofer, like a 12" woofer.

But if you're running a crossover at 60Hz, you're somewhat neutering the main speakers anyway, so it might not matter, in your case.  Some people run their speakers full-range and then use a sub or subs to augment the extreme lows, underpinning the mains, instead.

Basically mentioned above, but also the larger driver exhibits less distortion at higher levels.

There should be some videos of a guy testing just this, comparing various driver sizes and building various cabinets sizes to make them equal.

I find slam is generally associated with mid-bass (~60Hz) and above because the wavelength is shorter. Deep bass has a longer wavelength so it’s smooth bass or felt as pressure. Then again it’s relative because Arendal can use an 8" driver and a smaller cabinet to get more slam but sacrificing lower extension.

Generally though you’ll find an 8" driver in a floor standing speaker will be more smooth than a 6.5" driver above 30Hz. That's likely due to a larger cabinet and lower extension design.

With a 60Hz crossover, it’s probably a discussion of preference and there’s no way to really answer which speaker sounds best to you in that range. You also have to factor your preference in the high frequency, which is huge.

Personally for mixed movie / music use in a general living room, I like speakers that offer the most flexibility, which means larger drivers and a bright sound signature.

Almost any well-deigned floorstanding speaker will have no problem getting you down to 50Hz, so bass is probably the least of your worries in terms of things to worry about in terms of upgrading.  Two speakers I think would be an across-the-board significant upgrade would be the ATC SCM40 or Joseph Audio Profiles just to name a couple.  The 40s in particular have their muscular dome midrange that’ll likely up dynamics from the lower mids on up significantly over what you have now (assuming you have the amp for it), and here’s a link for the 40s just fyi, and best of luck. 

https://thesourceav.com/products/atc-scm40