Sensitive enough speakers for low power SET

Check out the "Teresonic" website. Also "Sonist", and "Decware".
"Reference 3A" is also a candidate, but not for 2A3 unless in a small room and you like simple music,300B would be fine. The trick is to find not only a sensitive enough speaker, but one with a simple crossover or better yet one with no crossover such as the Teresonic. Also the impedence of the speaker should be smooth and not go too low.I heard the Teresonic's top of the line speaker hooked up to a 2A3 amp and was totally blown away, especially the bass output was incredible! I think that the retail price of that speaker was under $15000.00. I have the Sonist Concerto 2's and I'm running them with about 5 watts in a small room and they will get real loud!
You should be looking at speakers with an SPL rating of 95db- 1watt@1meter or better. Good Luck and have fun!!

Second the Coincident. Several advantages to high efficiency speakers such as ease of load for the amp and oft very good low volume level resolution.

WLM

I am not sure about prices in the USA, but the WLM Gran Viola MkII might just fit your budget (unless the exchange rates wreaked havoc). Otherwise look at the Lyra MkII or Aura. These are ingenious speaker systems that can be upgraded (see the "Super-Pac" option) and adjusted to fit just about every room, and ... 97-98 db 1W/1m is standard at WLM.
http://www.wlm-loudspeakers.com/indexengl.html

Besides of WLM, I second Zu (whereby, I only know the less expensive Druid MkIV myself)

Good Luck

I have Zu Definition 2s and have heard Audio Note speakers. Both are SET friendly.

Klipsch