Shocked. Need Opinions. How muck power do I need?

In the context of the OP’s speakers and listening room it may not be obvious at first how much power/which amp is really needed, until the perceived experience sets in through a variety of different amps. Crank it as loud as you could possibly want, and then some, and then try and assess whether there’s a sense of headroom still (the limitation here may as well be the Dali’s). Knowing what proper headroom can do in these situations requires of one to, well, know about it through actual experience; what may seem at first like (proper) headroom, if it even registers as a priority, could easily be challenged in another, more capable speaker/amp context.

Or, maybe the proper headroom scenario turns out to be of secondary importance in the bigger scheme of things, and it really just comes down to the preferred overall sound at "normal" or more typical listening levels, even if it means giving up ultimately control and a sense of ease at higher SPL’s. If you can have both, however, that would be the preferred scenario.

Just today listened to the Leben CS-300F (~15W per channel) with a pair of hORNS Universum speakers, and it proved plenty capable and very lively in moderately sized spacings and a speaker sensitivity closing in on 100dB’s (in this case with the Eminence Kappa 15C as the woofer element; the later iteration uses a less sensitive woofer at ~95dB’s). Remember, your Dali’s would need some 20x more all-things-being-equal power here for the same perceived SPL, and even so the Leben with the Universum’s would likely seem like a small monster be comparison.

this the most interesting thread I have read in a while and such good answers to the OP's question.

I have a theory that has borne out to be true to my ears and understanding as an eleectronics tech and just the different amplifiers I have lived with. Like many people, my original audio setup was very modest, at 5 wpc using a Heathkit stereo receiver, it was replaced with a 40 wpc (Dynaco SCA80-Q) and then a Hafler DH-200 at 180 wpc into 4 ohms, then an Adcom 325 wpc amp, and finally a variety of Carvers at typically 650 wpc (1.5t) was my fave of the bunch - The Carverrs were all 450 wpc or above and always each step taken up the power scale produced to my ears better sound at any level. So my theory is if your speakers are rated at 300w continuous than an amp of double that power is sufficient. This way amp will never struggle to handle the load no matter the source material being played, and it will never go into clipping or even close to it. This protects tweeters and provides the best possibility of clean output from the speakers. Anything less is a compromise.

@livinon2wheels while I agree with you that Amp should be about double power rating than your speakers MAX Contin. power, lately I started to think that if your speakers can deliver maximum power without the distortions and sound is way too loud to sit and listen to it than you got correctly working system.

My 250W amp is pushing enough power and staying in class A, that I have no desire to ever turn it up. 

My speakers are rated 300W max but I think 50W class A amp will do Just fine.

So it's not a power output that matters it's the current levels that count and power banks size.

Although I’m not sure about the accuracy of the VU meters on my former Vincent hybrid amp, but it  never used over 3 or 4 watts during any of my listening sessions typically up to 80 db measured at 10 feet.  This is driving 87db sensitivity KEF R11 speakers.  I’m now running a Linear Tube Amplifier (Class A/B tube amp) with 51 wpc and never have had any problems. 

this the most interesting thread I have read in a while and such good answers to the OP's question.

I have a theory that has borne out to be true to my ears and understanding as an eleectronics tech and just the different amplifiers I have lived with. Like many people, my original audio setup was very modest, at 5 wpc using a Heathkit stereo receiver, it was replaced with a 40 wpc (Dynaco SCA80-Q) and then a Hafler DH-200 at 180 wpc into 4 ohms, then an Adcom 325 wpc amp, and finally a variety of Carvers at typically 650 wpc (1.5t) was my fave of the bunch - The Carverrs were all 450 wpc or above and always each step taken up the power scale produced to my ears better sound at any level. So my theory is if your speakers are rated at 300w continuous than an amp of double that power is sufficient. This way amp will never struggle to handle the load no matter the source material being played, and it will never go into clipping or even close to it. This protects tweeters and provides the best possibility of clean output from the speakers. Anything less is a compromise.