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


I’m considering changing form parasound a21 to Manley Mahi monoblocks (40 watt tube) to go with my Monitor Audio gold 300s.

the speakers (90 dB sensitivity) say they want minimum 100 wpc.  

What kind of problems (any?) will I run into?
otherones
celtic66, every recording has a "right" volume. And that right volume is multi-factorial. It depends on the type of music, the way it was recorded and mastered, the way your own system is equalized and the way our ears change frequency response with volume. Bass and treble increase with volume (see Fletcher-Munson). A recording that was meant to be listened to at loud volumes will sound dull and lifeless at low volumes. Turn it up and it sounds great but if you tried to play a string quartet that loud the violins would slay your ear drums. Rickie Lee Jones albums were recorded on the bright side and sound best (more natural) at moderate levels. Turn it up and her voice does that violin thing. I have an old Buddy Miles album with some great songs but it always sounded lifeless to me. I hadn't played it probably in decades. At 95-100 dB the record is a knock out. They were probably stoned and had the monitors turned up to the max when they mastered it. 
A word about listening to loud music. Always warm your ears up. In your middle ear you have a muscle called the Stapedius which dampens the Stapes bone keeping it from vibrating as hard against the oval window. Google it and you can see the anatomy. When exposed to loud sounds your brain tightens the Stapedius through the 7th cranial nerve lessening the amplitude the inner ear sees (hears) but it takes a little while to tighten. Don't just go right to 100 dB. Start off at 85 dB and crank it up 5 dB every few minutes till you get where you want. Beyond 100 dB is no man's land. It also takes a while for the Stapedius to let go which is why after a loud concert you can't hear anything for a while.
celtic66 quantity and quality are essentially the same or so closely tied that you can not separate them. The quality is not there unless the recording is played at the right volume which is determined by all those factors above. 
I really appreciate all of the discussion. My local store let me borrow the Mahi Mahi over the weekend and I spend a good amount of time playing with it and swapping back and forth to the Parasound A21. For additional context, my Preamp + Phono is also a Manley (Steelhead).

The room I am in is pretty small and the speaks only 8ft or so from listening position. I did not have any problems getting good performance out the power of the Mahis.... even in Triode mode things sounded great. UL bumped up the power but I suspect for most of my listening (jazz and acoustic vinyl) I’ll be playing in Triode.

At the end of the trial, I’ve decided to keep the Mahi Mahis and will end up selling him A21s at some point. Not sure if the Manley Steelhead being of the same manufacturer is part of it but the combo is sweet.



Now it's my time to crow; everything is just like I said, "Tube watts are louder than SS watts, plus they sound better"

Also, the room is the dominant factor; unless you got a huge room, you don't need all them watts.

When I'm right, I let everybody know it; but most importantly, we have another contented audiophile.
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.