Same watts at 8 and 4 ohms?

While it is true that 'speaker sensitivity plays a role in required amplifier power, it is also true that amplifier power capability plays a role in distortion.  An amplifier will exhibit lower distortion at low output levels than at high output levels.  Distortion will often rapidly increase as the amp's rated power is approached.  Linearity is usually much better at small signal levels, hence lower distortion. This means that at a given output power level, well-designed high-power amplifiers typically exhibit lower distortion than lower-powered ones.

I run two channels of four Harmon Kardon Citation II tube amps each that, on the bench, deliver over 500 watts/channel with 0.05% THD at 1 kHz if line voltage is held at 120VAC.  This means at normal listening levels, each amp is operating at or close to small-signal operation.  Since the 'speakers driven by these amps are B&W 802Ds, I am glad I have the high-power capability.
Normally, solid state amps will deliver twice the power to 4-ohm than to 8-ohm loads.  However, power supply limitations can limit 4-ohm output.  Tube amps generally deliver the same power at 4- or 8-ohms provided the secondary winding of the output transformer has a tap to match the 'speaker's impedance.
By the way, at age 77, it is getting to be a big burden to carry a 60-pound tube amp from the first-floor listening room to the second floor test bench every time I have to change a tube.  I do so because I set the output tube balance for lowest THD.  If anyone wants to make an offer for 10 Citation IIs (I have four spares but want to keep a pair for other use), please let me know.

Norm

George, the amp I was referring to is the Proceed HPA2. It is functioning fine and is in my primary system with an AR tube pre and Areial Acoustics 7B speakers. I'm keeping all of that as long as it keeps running.

The 6Ts are for a secondary system in my living room, primarily casual listening. The reason I'm looking for an integrated with DAC is that it all needs to be as small and discrete as possible to make my wife happy and integrate with Sonos Connect (so coax or optical-in are important).

Most amps you've mentioned are class D so George will do what he does bash class D using a Behringer PA amp as his usual suspect for all class D. If you want boat anchors you're all set but with your criteria of placement and price  most small discrete integrated amps will be class D. There are a few AB the Micromega M100 is class AB in a small package as well as a few others. The NAD C388 should work fine with your speakers. The little 316Bee you mentioned measures 4 and 8 Ohm the same, it's the way they use their power supply with the modified Ncore amps. McIntosh uses autoformers on some integrateds they measure the same watts into 2,4,and 8 Ohms. George won't like the McIntosh either. Here's specs on the 316Bee notice the same 40w at 4 and 8 Ohm. 

• Continuous output power into 8 ohms and 4 ohms
  40W (ref. 20 Hz-20 kHz at rated THD, both channels driven)
• THD (20 Hz – 20 kHz)

<0.03 % (250 mW to 40 W, 8 ohms and 4 ohms)

• Signal-to-Noise Ratio
• >95 dB (A-weighted, 500 mV input, ref. 1 W out in 8 ohms)
  >97 dB (A-weighted, 500 mV input, unity gain in 32 ohms)
• Clipping power (at 1 kHz 0.1 % THD)
• >45 W in 8 ohms
  >60 W in 4 ohms
• IHF dynamic power
• 8 ohms: 90 W
  4 ohms: 120 W
  2 ohms: 170 W

djones51 -- You're the first to mention McIntosh autoformers which raises a question I've been puzzling over... I have a wonderful pair of Magnepan 1.7 that sounded great when I reviewed them through the sellers McIntosh tube amp, (I'm not sure of the power).
Bringing it home and hooking it up with my Peachtree Nova Pre and 220 (class D) amp, it sounds very good but not as great in my recollection. Of course room size and positioning come into play but now I'm wondering if I'd get better performance by upgrading to a McIntosh or other high powered (AB) amp.

If your amp puts out 150 watts into 8 ohms and 200 into 4 ohms, it will drive your speakers just fine if you only need 100 watts into the 4 ohm frequencies to drive them as loud as you want to listen to them.

Is that right, @atmasphere ?

It is- and more to the point, in this example above, even though the amp doesn't double power **at full power** into 4 ohms, we can easily see that it does increase. If this amp has feedback, its output impedance will be low enough to enable it to act as a voltage source- all the way up to its rated power into 4 ohms. So what if that isn't double the power of the 8 ohm rating?? We are only talking about the amp at full power. At any other power level it will be just fine, meaning that it will indeed double power as the load impedance is halved. This holds true for impedances of less than 4 ohms too- but one must be increasingly aware of the limitations of the amp when coupled to such loads. As long as the load is easy to drive (such as Wilson speakers, which are easy despite their low impedance in the bass) it won't be an issue.


Now someone touched on a different issue- that lower impedance loads cause amps to make more distortion. This is true, and is why you really don't want to make an amplifier (especially a solid state amp) work hard for a living! When it makes more distortion, especially if solid state, most of that will be higher ordered harmonics and IM distortion, both to which the ear has a keen sensitivity! IOW if **high quality audio** is your goal, regardless of your amplifier, a higher impedance load will do better justice to your amplifier investment. OTOH if **sound pressure** is your goal, you have that slight 3dB increase in volume if your speaker is half the impedance. IME the latter isn't worth it, but I like the stereo to sound nice :)