Shocked. Need Opinions. How muck power do I need?

Independent of the quality of amplification, the quantity you need is actually really small if one is listening at a close distance. The speaker sensitivity is the key metric for power requirements.

The simplified math is:

1w of power can deliver the speaker’s sensitivities volume (e.g. 86db) at 1m (3.28 ft) listening distance.

For every decibel volume increase above 86db requires double the power.

For every meter distance requires double the power.

Therefore…

If one sits 5m (16.4 ft) away from a rated 86db sensitive speakers and wanted to listen to their music at 86db, he/she would 5w of power.

If the volume is increased to 87db, 10w of power is required.

88db would require 20w

89db would require 40w

90db would required 80w and so forth.

You can see there’s an exponential growth of power required when both distance and volumes requirements grow.

That said, the rated speaker sensitivity db, typically around 84 to 96db, is a very high listening volume for most audiophiles. A lawnmower is typically around 94db. Took a measurement using a free dB phone app and I’m usually listening to music around 60db to 75db.

Is 40W enough? Yes, your 75W Cambridge EVO75 (89.5 db sensitive) is powerful enough to drive your Dali Mentor 6.

You need ~4w of power to drive the speakers at 10ft listening distance at 89.5db volume.

Unless your speaker are super hard to drive, don't get too caught up in the quantity wattage.

It's more important it's quality amplification that can actually reach up into its peak numbers with low distortion… because what's the point of the power if it's not really usable power. Pure wattage numbers is mostly useful for marketing and sales.

@swede58 well thats even better, meaning that 20W does the job 

@erik_squires, i will track down the pass article. i would add parasound as an amp which does well with challenging loads--during my brief forays with 83db planars my 125w hca1000 was surprisingly capable.

For every decibel volume increase above 86db requires double the power.

For every meter distance requires double the power.

Double the power will increase volume by 3dB (+23% perceived loudness)

Volume drops at double distance by 6dB. To keep volume the same requires 4x power.  To keep volume at 2m the same as 1m requires 4x power.