High Efficiency Speakers 4 PC

I am putting together a new PC for near field monitoring and need a high efficiency speaker I can drive with a single digit tube amp. What I prize is clarity, imaging, and frequency extension. Also the highs must be smooth and transparent.

Thanks in advance.
You probably won't need as high a sensitivity as you might think from a pair of monitors that you will be listening to in the nearfield. I have a pair of Soliloquy Sat-5 mini-monitors downstairs from my listening room in my kitchen. I was surprised to find that I can drive them with most material to very rewarding volumes with only 9 watts from my SET amps. I had tried this in a larger space at greater distances and it was a complete failure as soon as I demanded any volume from them. At nearfield it works just fine. I believe they're rated around 87db at 8 ohms. Judging from your main system and your query, your budget and demands may be higher than my kitchen speakers yield (which I listen to while cooking so am not too critical of them), but I'd suggest not limiting yourself to only high-efficiency speakers if you are only planning on using them nearfield. If you do want the versatility of listening afar, among the respected high-efficiency monitors are Reference 3a DeCapo i which is rated around 92db as I recall. They might be a good place to start.