Looking for speakers for my 4W SET amp

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.