30 year old player, worth an upgrade?

Nothing wrong with my 30 year old Marantz CD40 player but is feeling an itch to upgrade.
My current amp is the Bada Purer 3.8Mk hybrid bought new 5 months ago.
Will any of these players provide a definite improvement in sound quality?
1) Nad C568
2) Bada HD23
3) Marantz CD6006 (used)
I do not have a chance to home audition any of these so would appreciate any inputs you may have.
The first two retails at about the same price while the third is about 40% lower.

"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.