More power for moderate listening levels?

how does one assign a nominal single value in ohms to describe the impedance of this speaker?

Everyone does it different I imagine. 'Nominally' this looks like an 8 ohm speaker- if so that throws off my efficiency calculation by about 1.5dB. The impedance curve looks fairly benign, which is good. Its really the efficiency/sensitivity (which since its nominally 8 ohms are about the same thing) which is the issue here. Its assumed from the plot that the amplifier won't make a lot of power driving the impedance peaks- since the amp is a voltage source and the speaker is intended for that. 

My Klipsch KLF 20 with 100Watts Denon receiver sounds better, more live and dynamic with electronic and dance music than my Gershman Grand Avant Garde powered by 125Watts Plinius SA 102. As someone suggested, a separate system for dance music may be a cheaper solution if you have a space. Used KLF 20 and 100Watts receiver (or int amp) will cost $1000 or less.
By the way, my Harbeth C7ES sounds good at moderate listening level, but when cranked up with 125 Watts class A amp, it sounds stretched and nosisy. 

@atmasphere 
@twoleftears 

I purchased the Pass based on the measurements given by stereophile as well as reports of folks achieving great sound with lower power tube amps driving the Shl5. So far so good. With the volume halfway, the sound at my chair is fantastic with no strain. I'm a big fan of the sound when these two components are put together. The limitations of the system become apparent at much higher levels and with certain types of music. My assumption is that the bigger Pass integrated would clean up the sound at higher decibels and would be a measure of protection against speaker damage if one of my family members decided to crank it when I'm not around. Aside from the balanced design of the bigger Pass, does the extra headroom power-wise afford better sound at the levels that I normally listen to? For that matter, what are your opinions on balanced vs. single-ended designs? I would also be able to use the balanced outputs on my DAC.

As per Stereophile: XA25 80 watts into 8 ohms; XA30.8 130 watts into 8 ohms; and you can go up from there.

My assumption is that the bigger Pass integrated would clean up the sound at higher decibels and would be a measure of protection against speaker damage if one of my family members decided to crank it when I'm not around.

It will help. But keep in mind that to go from 80 watts to 130 isn't even 3dB, and 3dB is a slightly higher volume level- its not much. You need about 10dB to seem like its 'twice as loud'. This phenomena has a name in the electronics world- its known as 'gold-plated decibels' since the price of an amplifier needed to really do the job, that also sounds as good as the one you have now, goes up exponentially. That is why a more efficient speaker is the better investment dollar-wise (and sound-wise). 

For that matter, what are your opinions on balanced vs. single-ended designs?

I'm a big fan of balanced designs (and my company was one of the first to offer them to home audio; we made the first balanced line preamps made anywhere). So my perspective might be considered skewed. But balanced circuits tend to have less problems with power supply noise and offer the potential for lower distortion as even ordered harmonics are cancelled. This means that the 3rd harmonic is the primary distortion component, and the 3rd is treated by the ear the same as the 2nd (adds a little 'bloom' but is otherwise innocuous and inaudible), but it will be at a much lower level than amps that tend to generate a 2nd harmonic as their primary component (for you math nerds, the difference between a quadratic non-linearity and a cubic non-linearity). This means the circuit can be more neutral, as the ear treats all forms of distortion as some form of tonality (hence the 'bloom' I mentioned). If the circuit is differential in nature, it will also have less noise for any given amount of gain; by a maximum of 6dB per stage of gain.


Now when you run balanced, you also have the opportunity to run balanced line interconnections. The advantage of this is that the balanced line connections have far less sonic artifact than single-ended cables (if you've ever auditioned the latter and heard differences, you know what I'm talking about) but this aspect is only realized if the equipment supports the balanced line standard, known as AES48. Most high end audio equipment doesn't seem to support the standard; my theory for this is either the manufacturer does not know it exists, regards it as too expensive, or sees it as an impediment because there are really very limited ways to do it correctly (one of the better ways to do it is with an output transformer, for example at the output of a preamp). But its nice to be able to run 30 feet of inexpensive interconnect, so you can have the amps right by the speakers and run short speaker cables- this advantage alone results in immediately audible greater resolution! Its nice to get off the interconnect merry-go-round at the same time.