High Efficiency Options?

That sounds like great fun. A few years ago I decided I really wanted to experience a 300B amp. I had upgraded my headphone system in other respects… so I upgraded my headphone amp to a Woo 300B headphone amp… I fell in love with the sound. 
 

The problem was my main system didn’t sound as wonderfully musical as my headphone system. Well $70K later my main system sounds that good. Really happy I took the real tube route. My systems sound so much better than I ever thought possible. My systems are shown under my user I’d.

@ozzy62 is right.  You need a speaker in the 90db range for sensitivity.  Klipsch heritage series are one option to consider.  No direct experience with Omega that @rar1 mentioned, but full rage speakers are often a great option for tube gear.  These often do very well in terms of imaging and midrange reproduction.  The Omegas are crazy efficient at just short of 95db/watt/meter.  

@brylandgoodman,

Even if you aren’t going to listen loud, higher efficiency translates to better micro and macro dynamics even at lower volumes.

I agree with the above statement @ozzy62!

I don't think you will find a true high sensitivity, 8Ohm speaker, for $1500 a pair, if you did there would be no useful output below 55Hz. With that said I do like Zu speakers, but, 1500$ for a pair? OMEN DIRTY WEEKEND MK. II maybe. To me high efficiency is 2.7% or higher, remember efficiency is not the same as sensitivity. See below efficiency and sensitivity ratings.

Mike 

I think it would be hard to make valid suggestions without more information from the OP.

Does he want to stick with the tonal balance and sound that is similar to Harbeth? His other components like the DAC also lean towards a warmer musical presentation.

When he says low power, how low ... 3 watts or 10 watts? 

Perhaps the OP has an amp in mind that would give forum readers a better reference point for speaker matching based out of their experiences. What tubes does it run output? 300B tubes or 6bq5s? Both sound very different.

Finally, what kind of music and at what volume does he listen to?

How small the your bedroom? One man’s small is 10 x 10, another 15 x 15 with high ceilings. The volume of the latter is almost twice that of the first and you would need more efficiency and/or power to fill the room.

i once owned a pair of the Harbeth C7s and despite what the specs said, they needed a fair bit of power to sing and worked better with my 100 WPC SS and than my 45WPC tube amp which is not what I expected. I liked the C7, based on a very favourable review without hearing them but they were not the sound for me, and buying used I moved them along at no loss. 

Here's an idea. Buy your new low powered amp and try it with the Harbeths you own in your bedroom. If you think that works then you will know if a speaker of the sensitivity of the Harbeth will work fine. If it doesn't you can go with more efficiency.

Many readers use and will suggest Klipsch as a match for low powered amps. They are extremely efficient and are a good match, BUT, they don't sound anything like a Harbeth.

Thanks for all the input. I am starting to check out Omega speakers, and so far I like what I see. 

Far as how low of power, I’m really not sure. I don’t have an amp in mind at this point but probably a set amp of some sort. You guys are probably right that I’ll be better off with something over 90db to give me good flexibility with my amp selection.  I think I want to find speakers first and work backwards from there, but I’m open to purchasing an amp first. Right now I have a pair of Totem Rainmakers, and don’t think a SET amp would be to happy with them. That’s kind of why I was thinking speakers first. I unfortunately will have to buy one piece at a time and build slowly. 
 

The room is truly small, I believe 9x11 with 8 foot ceilings. Also I don’t think Klipsch would be a good choice for me with my tastes. I really prefer I nice full midrange and I’m willing to sacrifice elsewhere to achieve it. My experience with Klipsch was a pair RF5s, and found them fun but not my cup.  In this system I understand I may have to sacrifice significantly considering the budget I’m working with.  I’m hoping to eventually enjoy this system more than my main.  My thinking there is, smaller room = less money, SET = more magic, and also more uniform room with better placement options = better imaging and soundstage. 
 

Hopefully that gives you guys a bit more to work with.