30 year old player, worth an upgrade?

@ertorque:"

"The CD40 does not have digital outputs. It is the cheapest Marantz player that has the TDA1541A chip"

My bad-- I should've suspected that a CDP that old might not have digital outputs.

keep in mind, if you do go with separates, you'll have a lot more choices in terms of your preferred sound, due to the significant differences between DACs. 

A used Apollo-R, excellent sound on its own and can be used as a transport should you decide to move to an external DAC.

I added a $130 Topping E30 DAC to my 30 year old Denon CD player, and it made a notable improvement.

It certainly is. Digital sound quality has come a long way in the last 30 years. If you are going the DAC/Transport route, try to find a DAC that is less than 5 years old IRT technology. 

Thank-you for all the responses. At the moment, I have no intention of going separates but all 3 players under consideration have digital outputs so running them as transports + DAC in the future is possible.
In Malaysia where I am from, used hifi market is not as big and dynamic as that in the States, so a used Apollo for example will not be an easy find.
The price of the players I listed is equivalent to around USD650 for the NAD and Bada. The Marantz CD6006 would be 40% lower given that it is an used item.
So I guess my budget would be around USD 650~ 700.