recommend entry-level high-efficiency loudspeakers

Or JM Reynaud, perhaps?

Hammer Dynamics Super-12 kit - $650

98dB, 8 ohm, 12" fullrange driver with a super tweeter corssed in above 16kHz. This is a fantastic design by the late John Wyckoff that is still produced by his wife in rememberence of him.

I've owned one for almost 3 years now and have tried it with a variety of low power SET and PP amps. It is a stunning perfomer that achieves something very few affordable high-eff speakers can - bass slam/punch.

It is articulate, fast, tonally rich, and paints a cohesive musical landscape. There is a seamless integration from top to bottom of the frequency range. Has to be heard to understand. Cohesiveness is something that all good single-drivers do much more easily than multi-driver speakers.

Not to mention there are a variety of cheap tweaks that can be performed (or done from the beginning) that take it's performance to a very high level. The old Single Driver Website has a page dedicated to optimizing the Super-12's and there are plenty of owners around - search the Audio Asylum High Eff forum for posts.

Unfortunately, all the info at the old Single Drive site was lost(for now) when they changed forum software.

If you have any wordworking skills, it can built to commercial level quality for a low price. If not, you can still have a local cabinet maker build whatever you want and still make your budget.

I'm not saying that the Super-12's are the greatest speaker in existence, they clearly are not. But, they do so many things right at such a low price, that the next step up will cost you a pretty penny.

Over the years, I have heard several truly amazing high-eff systems. But, as good as they were, I just couldn't justify the huge expenditure since I was already getting great results with the Hammers.

It wasn't until a few months ago that I made the jump and it cost me dearly. Check my system here. BUT, I kept the Hammers for reference and nostalgia, they are good enough to sit alongside of(or in the same house with) $5-10k speakers when you consider the cost.

Is the new setup exponentially better relative to cost differential?

Honestly, I can't tell yet, I'm still in the setup and fine tuning phase. I haven't tried the Hammers with the dual subwoofers, new DAC, new turntable, new phono preamp, cartridges, etc. Maybe that alone would have been good enough for me.

I would second the Triangle Titus, very efficient and accurate. I replaced a pair of B&W 330i's with the titus to keep peace with the wife. I looked at many small speakers from VR 1's to Amphion Argons. The Argons sounded great to me but they were $2200 and I was able to pickup the Titus for $495 deliverd to my door. I have had them for a little over a year and for the money I have not found anything that I like better.

klipsch rb5 II is a bargain and a nice speaker...have to find used as it is discontinued; ebay best bet

Here's three more... $635.00 Fostex BK-16 Folded Horn Kit . Also you have the Full Rangers from Raw Acoustics.
Last but not least for $389.00 a pair
The Omega MiniMe .