Looking for speakers for my 4W SET amp

I'm looking for some speakers with very high sensitivity for my 4W SET amp.  This is for a 2nd system so I'm not looking to break the bank.  I'm looking into Zu Omen Dirty Weekend, Omega Junior XRS or maybe a DIY project with Audio Nirvana or Lowther drivers.  I've never owned single-driver speakers before and I'm a little nervous to take the plunge.  Any thoughts?

Omega XRS - I'd be more worried that this may take the place of your main rig. They have an intoxicating sound with proper amplification (set amp).

Get a used pair of Klipsch Heresy's - Mk1 or Mk2! They can often be found on EBay for about $400 - $500 + shipping. Sensitivity of about 99 db! That's where I bought my pair. My SET amp is a Sanei 560A with 2A3 tubes and all Tango iron, made in Japan.3.5 wpc. The Heresy's will KILL any of those single-driver speakers! They are capable of rocking out with just a few watts. Sure, the design is old (1957) but Paul Klipsch got it right!
Another vote for Omegas.  I've spent time with Heresys and if you want to "rock out" then those should be considered as well.  The Omega's have a purity that the Heresy's lack, but the Heresys will definitely play louder and do a better job of unravelling complex music if you listen at higher volumes..

I've got a pair of the Zu DW's as well, they are closer to the Heresy sound.  A little more raw, more bass, but they are fun, especially if you want to just turn the volume up and spend less time in the listening chair enjoying the nuances of a recording.
Charney audio is the best or VoXativ
Thanks guys.  I think I'm leaning towards the Omegas.  I listen mostly to jazz and classical so I think the Omegas would fit the bill.  I'm looking for a clean detailed sound with good separation of instruments and 3D soundstage.  Any thoughts on which Omegas?  I initially was drawn to the Junior XRS but now I'm looking at the Alnico monitor and the high output 3s.  Would they have enough bass without a sub?

" Would they have enough bass without a sub?"

That's a totally subjective call.  What's good for one person could be totally inadequate for another.  Also room size and placement and room treatment will play a big part in this.  If you haven't already, you should go to the Omega forum...there's lots of discussion about the different sounds of the various drivers.
Yes, Charney is great, and so is Voxativ, but, I think both qualify as "break the bank" (five figure systems).  For around $3,000 (new), Tekton Double Impacts and Rethm Bhaava are among the best high efficiency systems at less than crazy prices that I've heard.

There are terrific sounding moderately high efficiency systems that would work with a 4 watt amp, such as Audio Note speakers, but, extremely high volume levels cannot be attained with just 4 watts.  

I have not heard any low-cost single driver system that I really liked.  All of the really good ones--e.g., Charney and  Voxative systems, are not cheap.  I've heard some nice systems that were custom-built utilizing single drivers, but, the ones I find acceptable utilized really expensive drivers (AER, Voxativ, G.I.P., Feastrex).  
Hello adam, What amplifier do you have?
I would suggest calling Louis. With your music preference I am guessing he would suggest the alnico. I do not use a sub(s) with my 3XRS HO (:
isochronism,  I have an Elekit TU-8200 kit.  To my ears, it sounds best in triode mode.  Other modes are ultra linear and pentode giving 8W per channel but they don't sound as good as the 4W in triode mode
My Heresy IIIs required a sub or two (which I already owned), but add those and the Heresy IIIs are astonishingly coherent great sounding things, and relatively inexpensive.
There are a lot of choices.  A search on Audiogon will reveal a slew of threads.  My short-ish go-to list of SET friendly speakers include:
- Klipsch Heritage.  Heresy to Khorn, depending on your room and your budget
- Omega.  All good.  Speak to Louis for specific recommendations
- Coherent.  Great speakers from the great white north.  I own a pair of 8s and they are very good but I hear the 12s and 15s are fantastic.
- Diatone.  This is Japan's JBL.  A wide range of speakers in various sizes and configurations.  I don't think these guys ever made a bad speaker.  In the U.S. most models are branded as Mitsubishi (but not all Mitsubishi speakers are Diatone).
- Altec 17 and 19.  Big and bigger.  Other Altec models as well
- McIntosh ML-1C.  Don't laugh, these can sound quite good (in a vintage way) IF they are recapped and paired with the MQ101 equalizer.

4W is tough - depending on your space, how loud you like to listen, your choice of music, and even (perhaps) the length of speaker cables. It is right on the cusp.
thanks to everyone who contributed to this thread.  You've given me lots to think about
4W is tough
4W is more than enough, assuming that you select symbiotic gear and aren't trying to play in a concert hall-sized space.

My 45 Triode monoblocks put out 1.5Wpc and play plenty loud in my living room.  How many enthusiastic owners of decware UFO amps think 1.7Wpc is all they need?

You do need to pay attention to all the things gsm18439 listed.  As many have reported, I don't find that SET amps to be best for some musical genres like (obviously) heavy metal and techno.  Music with "too many notes" like large orchestral pieces are harder to get right on most/smaller single driver speakers.  But I have never heard a system that was perfect in every way.  Have you?

I have not heard the The TU-8200.  I have heard the TU-8600 (300B amp) and it is a terrific amp for the money.  I am a fan of the 6L6 tube, so I would bet that the TU-8200 is a winner.  I hope you find something that it will drive to a satisfying level.

From my experience, the kind of music that is hardest to achieve a satisfying or realistic listening level with low-powered amps is choral music, particularly acapella choral music.  At surprisingly soft subjective levels, the music seems to fall apart.

You are probably on the right track looking at Zu speakers--they are fairly efficient and easy to drive.  Zu's are very punchy sounding speakers; for some reason, the Zu representatives show them only with solid state amps, so I have not heard them used with low-powered tube gear.   Audio Note AN-K are nice speakers that are also not crazy expensive (they are warmer and more relaxed sounding than Zu speakers); I've heard them with fairly low-powered SET amps (7.5 watts/channel) and with push-pull 6L6 amps and they sound good. 

I have much preferred Lowther drivers used as wide range drivers (used as a midrange), rather than as a full range driver, but, they can be terrific as fullrange drivers in back-loaded horn systems.