Where to donate electronics in good working order

Goodwill or a local college with an electronics class

but... nad is good enough to sell

Salvation Army

Is168-

good advice as above. Any thrift store is a nice choice as well.

the 763 is notoriously failure prone. It is the low voltage caps in the regulated low voltage rails, which is generally the culprit. It’s the thing known as ’the capacitor plague’. Many companies were bit by it, to the tune of billions of dollars of A/V gear tossed due to bad caps.

https://en.wikipedia.org/wiki/Capacitor_plague

Habitat for Humanity.  The staff there generally has someone who will recognize 'the good stuff' and price accordingly.
I ran into a pair of Infinity floor speakers in mint condition going for what I thought was quite reasonable and would give H4H a 'bump' in the donations' take.  I didn't bite, but was tempted...*G*

If you live in the UK, try to donate through one of the charities. For example, I know that Little Lives UK has electronics collection service.