From Pass X250,5 to 350,5 : what to expect?

I have to agree with Ingvar. I don't think that sheer watts is the reason for a difference in sound. It must be that a different circuit or design or components are used to produce the higher power. Or like so many other things in our whacky hobby, there is something we are yet even aware of yet that has an affect on the sound.

spatine, what efficiency and nominal (and minimum) impedance of your speakers? You will be very surprised at how little power you actually need if you listen at normal listening levels. I actually calculated the power my speakers needed at varying volumes, listening distances, and peak music levels. I was surprised to just how little power is required.

spatine, what is sensitivity of your speakers and its nominal and min impedance? If I have this info I can calculate for you the max power you will need. Also, how far away do you listen?

The XA does not double down power.

spatine, assuming the sensitivity you provided is at 8ohm, here is what I calculated based on your numbers (these are only best estimates):

at an average volume of 70 db assuming a peak of +15db, you will need 0.03W at 4ohm and 1.0W at 85db

at 81 db average you will need 0.5W at 4 ohm and 16W at 96db.

If you speakers dip down to 2ohms. then double the power.

As you can see, you really do not need a lot of power. For you to use around 250W of power at 4ohm, you will need to be listening at 108db!

In opinion, most people do not need high power amps. However, as it has pointed out, sometimes higher power amps have better circuits or designs which produces higher quality power at lower output.

Note that these calculations were obtained from a spreadsheet I developed which has some assumptions, approximations, and estimations. For example, I assume it takes double the power to increase the volume by 3db. I also assume that the volume decreases by 5db for every doubling of distance from 1m.