how does current work in an amplifier?

Atmas,

I don't think the SS devices of 40 years or so ago can be compared apples to apples with their tube predecessors.

True, probably that SS was cheaper power technology than tubes, but most good vendors tended to maintain and add value with new features that could now be offered and still make a profit.

There is nothing evil about progress. It usually involves doing things more cost effectively in conjunction with providing greater overall value.

Its many years later now. Tubes have their advantages and disadvantages just like everything else. Their disadvantages overall led to their falling out of favor. Not to say that they are not capable of doing unique things in regards to sound quality overall still these days, but there is more than one way to skin a cat....

Atmasphere, with all due respect there were other incentives such as convenience and reliability amongst others.

Unsound, certainly! I think we can add to that, heat, as well (although I know of transistor amps that run as hot as tubes). We are talking about a very traditional set of tradeoffs when these aspects are brought into the conversation: convenience vs performance, an issue you see in nearly every field of endeavor.

Mapman, Of course semiconductors have improved immensely since the beginning of the art! I'm not saying there is anything wrong with 'progress' in of itself. I'm just pointing out a simple fact.

Dob, I like the idea of EPDR; like other specs it does not appear to tell the whole story, but certainly would standardize a lot of things that can be hard to winnow from the other specs you see. IME, Magnaplanars seem to have an easy EPDR rating compared to a lot of 4 ohm speakers I have seen. This would be very apparent if such a spec were commonplace.

Atmasphere, of course many of find some ss amps offer a balance of both objective and subjective performance that is preferable. I am confident that many speaker designers welcome the opportunity to avail their design talents towards making speakers for those ss amplification attributes for the sheer performance opportunities those combinations provide.

One possible solution to giving an amp some 'figure of merit' based on reactive loads is to Standardize such a load and let amps fight it out.

Also, I've seen an amp tested the following ways.
Into a resistive load....Try it at 4, 8 and 16 ohms.
Into a +45degree reactive load at the various resistances
Into a -45degree reactive load at the various resistances.
Afte the above, you can draw a very nice plot....would be a 3-d plot and visually tell how an amp performs into real world loads at a glance.

However, for easy of testing, the 'standard' speaker load makes more sense.
It could be reproduced anywhere at any time by any competent tech and the results would compare with all others using the same method.

But, that's just my take.