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 DAC's alone over the past 15 years are so far superior to what was available then.  There is a very interesting PDF running around from AKM that explains some of it. 
As a very happy owner of a Marantz CD6007, if the CD6006 is even close, it's a pretty great value. Marantz continues to impress as one of the few brands   bringing higher end build quality and electronic designs in at reasonable prices. 
It just occurred to me that my BADA amp has balanced inputs. Upon further checking, only the BADA HD23 player among the 3 under consideration has balanced outputs. Is balanced connection almost always superior to RCA? A downside of the BADA player is that it hasn’t got usb inputs but that shouldn't be a deal breaker for me.
Marantz CD6006 vs CD6007 different Dac chip and a handful of different components in the 6007 they are very close. Close enough to not warrant me upgrading ill keep my 6006 great player plus you get a half decent headphone amp. 
I recently had a similar problem when my old Philips CD player started to show its age when paired with my Sennheiser Headphone Amp and HD600 headphones.   It clearly showed what a mediocre player the Philips was compared to today's players.  I replaced it with an NAD C568 and have been very satisfied with the change.  Noting that the C568 is on your list, you might well have the same experience.  Good luck in your choice !