Not sure any lower cost av receivers have a really decent digital section. The ones I have heard are pretty poor then again so is my opinion of the nuforce. Now some of the older ones around 10 years old or so that were near top of the line may have a decent dac. Maybe you can pick one up for a decent price.
As for 30 year old receivers, they sound okay if you like a warmish type flavor. Personally, most $150 pro audio amps sound more open and revealing although without the features and warmer tone of the older receivers.
I am sure they can sound really nice but might be a bit worried about caps going etc. Then again if you can pick one up for under $100 I might go for it. Certainly would not spend more than that, they really are overpriced on ebay for example.