I've just bought a Delta 290 (which I think was the next model up from the 90 back in the day) for a second system based on an ipod - I've just replaced a marantz PM 4001 (which I think is/was about £150 at full price), going into MA BR2s, and it's safe to say that the 290 absolutely blows it away, so I'm sure that if the '90 is in full working order which it sounds like it is, it will very easily outperform your Denon.
Where it comes to amps, despite what the manufacturers would like you to think when they introduce a new model with a big fanfare and loads of claimed improvements, changes are very small and incremental, so a good amp from 20 years ago, is absolutely still a good amp today.