JustMe wrote:

I find this very interesting!

The consensus is that this is perfectly possible.

No reason why not really.

Could these filters be placed onto an IC and switched on the front panel?

I'd be inclined to use a decent DSP and allow it to be programmed from a
PC personally...

That way, I can have my "straight-wire" amp and switch between "Alchemist
APD6a" mode, "Keith's Chinese valve amp" mode, "Audiolab 8000LX" mode,
"Cyrus V" mode, etc.

Yup.

Nick points to a box which seems to not only reproduce the qualities of
amps, but speakers too.

How can this be?

I dont see how it can be since to do so the box would need to have
knowledge of (at least) your room acoustics and speaker properties, and
(preferably) the room characteristics the 'target' speaker is used in.

(on top of that you'd need a profile for the other speaker, of course.)