calling all Guru;s, Ideas on audiophyle high effeiciency speakers solicited

Loved the sound with the Krell, would not mind trying a more efficient speaker with a tube sys but need to know what to look for

You're speakers allegedly have 90db sensitivity with a nominal impedance of 8 ohms. In theory, that's fairly efficient by today's standards, and should work with a tube amp of about 50 watts. After all, B&W recommends a minimum of 50 watts. However, it seems most B&W owners end up settling with powerful SS amps. 

If you want to try tubes with your B&Ws, I have no doubt that a Rogue Audio Cronus Magnum will drive them to sane volumes. That's about the most glass power one can get for the money. If your heart is set on low power SET amps, you'll need different speakers, ideally some of 94db sensitivity or greater.

 Some will tell you that tubes necessitate 3-digit sensitivity. That's complete rubbish. I can drive my 87db spec speakers to loud volumes with 45 tube watts. Also, room gain, listening distance, music genres, particular amp design, and desired headroom play a significant role.

Contrary to untutored belief tubes are NOT inherently better than transistors! I own many amps of both types! Your 803D2's are truly excellent speakers and capable of better sound than ANY high-sensitivity types. I can recommend a New York Audio Labs NYAL Moscode 300 (tube/MOSFET hybrid) to power the B&W's. A superb amp designed by George Kaye - and capable of handling difficult loads! And being a hybrid it will give you a nice taste of tube sound - without the drawbacks of an all-tube amp!

I can speak from experience, owning a NYAL Moscode 150 (half the power of the 300)!

High eff is over 100db medium about 90+db up ohm load also effects ability to drive and must be considered. Most high eff designs use large cone area many need to be multiway over 3-5 way depending on end goal and range required. I would suggest you select tube amp maybe list budget system room and over all system goal you wish to achieve if you want more detailed information. I would say pursuing higher efficiency can be a laudable goal and can yield incredible sound over conventional systems but users need to have a bit more knowledge when selecting such over what one needs for standard audio fare.