Speaker wants 100 watt RMS. Is 40 watt tube OK?

I rest my case.  Mahi Mahi mono blocks are so good.  And Manley Labs is correct.....Tubes Rule!  Never had a doubt.  Now you can play the tube rolling game with Upscale Audio.  

It is mind blowing how different these amps sound with tube and power cord upgrades.  I run Patrick Cullen.  You may like others.  The timbre, resolution and attack of the amps will change appropriately with upgrades.

The Steelhead is great and voiced well for the Mahi, but you may not need to go beyond the Jumbo Shrimp (no phono).  That was my match up until the Manley Neo Classic 300B with Takatsuki 300B tubes.  Enjoy the ride.  

You have done well grasshopper.

Orpheus10 , you are right. Tubes gives a louder sound, but more correct. When the tube-amp is 40 W, than he gives constantly 40 W. I had a Copland 405 tubes (25w) ,with the Audio Monitor PL 300 (350w): In a room of 55m2. It sounded incredibly beautiful. You gonna enjoy it!!!!  When you play exactly 10 W in your room ,after an hour ,  you go walk in the park ,because it’s very loud

Please correct me if I'm wrong as I am not an expert but I have always felt that that the higher current amps give much better control over the speaker. Damping also plays a critical role. I feel like watt ratings although important are usually a marketing term to ill informed consumer.
 

Please correct me if I'm wrong as I am not an expert but I have always felt that that the higher current amps give much better control over the speaker. Damping also plays a critical role. I feel like watt ratings although important are usually a marketing term to ill informed consumer.

Actually no speaker needs more than 20:1 for a damping factor and many need less. If the damping factor is too high the speaker is overdamped and an unnatural phenomena known as 'tight bass' occurs. Many audiophiles like tight bass, but its a coloration.

I can tell you on my experience using 50 watts manley stingray with thiel cs 6.3 and even with larger cs 6s. Stingray perfectly drived cs 3.6 s for many years. Later i used 200 and 300 watts solid state amps with the same speakers. I cannot say that there was a luck of power from stingray