@horta, I found it strange that Decimator had gone away, so I checked. As it happens it's not a native Audacity plugin, but it' part of Audicity "sponsored" pack of additional plugins that can be found here fosshub.com/Audacity.html/LADSPA_plugins-win-0.4.15.exe . So doubly thanks for bringing that up (noticing the lack of Decimator and providing the Nyquist code for down quantizing).

Even worse, then. Some separation can sometimes achieved by a phased approach and error and trial, aplying a variety of different techniques. A fully automated system is still pretty far away, I think.

Good pointer @MarcW, it helped me understand the arithmetic behind the 44.1 figure, which I didn't know, thanks for that.It's a pity it doesn't explain the reasoning behind Philips' proposal. Anyway I didn't meant that there were no possible alternatives (upfront it could have been any value greater than 40KHz plus a few KHz for the low pass filter transition band), only that the precise 44,1KHz value was eventually chosen, as the article states, "To enable reuse with minimal modification of the video equipment, these ran at the same speed as video, and used much of the same circuitry."

Your explanation shows why a somewhat larger than the strictly audible (in theoretical ideal conditions) 40 KHz was necessary, but as I recall, the precise setting of 44.1Khz is not magic value, it was simply inherited from some previously existing Sony component (possibly related with professional video cameras, but I forget), when designing the first CD system together with Phillips.

Very roughly, yes. If that's the case a 20 to 30W amp will probably be adequate to your speakers. Take care allways comparing same power units (peak power or RMS power).

That's a good point @MarcW, the OP does not mention it and in my answer below I did not consider the possibility that the source tape might be in stereo. If that was the case it would be indeed a shame to loose the stereo audio.