>It doesnt make sence to convert analog do digital and then play it
back on a vintage quad amps.

Why not?

If you decode it from analog and record the digital results you are
stuck forever with that one decoding on that one decoder. Plus, you
have to spend a whole lot of money on the equipment to encode multi-
channel digital.

But if you just do the best possible recording of analog to digital
stereo of quad encoded material you then:

1. save wear and tear on the original analog source material
2. have the option of listening to the material on a variety of
differend decoders that you have now or might acquire on the future,
plus you can change the settings if the your equipment changes.
3. Don't have to buy a super expensive sound card and encoding
software.

Personally, I like to hear the same source material in different
decoding environments. AT the moment, one of my favourites is to
take stereo source material and use PLII to matrix it out to 6.1 and
it would make no sense for me to do that once and record the results
into digital 6.1, if for no reason other than the fact it would be
ridiculously expensive and I would be stuck with that one particular
set of PLII settings, concerning width, panorama, etc. But if I just
digitize the raw analog, I can play with it forever in all the
infinite variety of settings that I might chose down the road as my
ears, equipment and furniture change.

No?