For efficient speakers, how much difference does an amp really make?

"I have zero interest in debating my recommendations". Doug, you just blew the wind out of a few sails here!! Kudos

Not all amps of a similar power rating are created equal in terms of ability to drive any speaker well.

Usually amps with ability to deliver more current will perform better with more challenging speaker loads regardless of efficiency rating, which are common these days.

The indicators of an amp like that is ability to double current delivery into 4 then maybe even 2 ohms and usually have higher associated Damping factor, more like 50 or higher rather than lower.  Some amps, the ones I tend to like most,  may include explicit current delivery capability specs.


Used to be these amps were also big heavy and expensive if Class A or even A/b but these days not necessarily the case. Some very efficient Class D amps with better power supply circuitry can deliver a lot of watts and current when needed out of a smaller lighter box. The efficiency of the amp essentially helps compensate for the inefficiency of most speakers out there these days.

Both BEl Canto Class D amps I use are good examples. Look up teh specifications of teh Bel Canto ref1000m amp for example.

Another significant factor has to do with output impedance of pre-amp used. Not an issue with most SS pre-amps however tube-preamps have higher output impedance which means a SS amp it mates to should also. 60-100kohm or so input impedance is what to look for. Some amps are designed this way to work well with tube pre-amps, some are not. Good impedance matching from pre-amp to amp minimizes distortion and general results in better clarity and definition top to bottom.

Regarding Ascend Sierra speakers specifically, I am not familiar with those but the specs I see on the company website for these models in general seem to suggest moderately more efficient than many at best and that they tend to go for somewhat extended bass for their size which almost always means a few extra good quality high current watts could only help since they have to work harder to deliver flat extended bass from a smaller package. A 300 watt continuous power rating is a good indicator that the speakers should be able to handle pretty much as much power as you could ever practically throw at them.

Current is king. An amp that is comfortable at 4 ohms and stable to 2 ohms will be able to drive those with authority. An amp that is stable at 4 ohms and nothing below will likely sound thin as volume increase. I had this problem in the past with an integrated that was 4 ohm stable but not really happy there and with a power amp.  
At the time I upgrade to a Rogue Hydra (100w class D and doubles output down to 2 ohms) and my speakers came to life.

Because I import Art Audio, I brought in a pair of $17K mono-blocks and not shockingly, they have plenty of current to handle my lower impedance speaker.  

many manufacturers put in a power supply that delivers a big number into 8 ohms but won’t be up to the task as impedance drops. 
At times you can find that Hydra in the $1500 to $1800 range.  A stereo 100 which will have 50w in triode, 100w in ultra-Linear would be another great choice for hybrid and tube gear.  
For Solid State, Musical Fidelity is a strong value and does well at 4 ohms.  If you can find a used M6 PRX, they are amazing.  A new one is $2300 I think.  The older ones were $3K.

My take - the more efficient the speaker, the more the balance shifts toward quality from quantity when it comes to amplifiers. 

For a given budget, any amp designer is going to have trade-offs between power and finesse. There are obviously going to be some designers/companies that are more creative/efficient, etc. but building a more powerful amp means higher voltage parts, bigger transformers and caps, bigger heatsinks, larger chassis, etc. which take budget away from higher quality components. 

In other words, high efficiency speakers do not, in the least, diminish the benefits of a high quality amplifier, but they do reduce the need for tons of power. If anything, a high efficiency speaker will expose the limits (noise floor, linearity, etc.) of your electronics much more readily than a low efficiency speaker. 

If you've got high efficiency speakers, take advantage of your lower power demands to get an amplifier with more refinement for the same budget.

High efficiency speakers done well is a good thing but good quality full range ones are big bulky and thereby relatively expensive and generally require a lot of room to breathe.  Not for everyone. 
No single approach can do it all best.  Hence the variety. 
Also, these days, high efficiency Class D amps are a game changer delivering more often for less and in a smaller easy to handle package that is practical for many.