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.
Why not keep the Marantz as a transport and put all your money into a separate DAC ?

Why not keep the Marantz as a transport and put all your money into a separate DAC ?
The CD40 does not have digital outputs. It is the cheapest Marantz player that has the TDA1541A chip.
Sounds great I will look for more on this topic to be better informed. volume_upcontent_copysharestar_border

Post removed 
Post removed 
Post removed 
with the CD6007 released, prices are good on the CD6006 and it should way outperform your CD40...I always found the expensive Sony DVD players to make lousy CD transports...
I don't know what your budget is, but I think that player has seen it's day as far as it's transport and the DAC. Remember, the chip is only part of what's important. The rest of the DAC and the way its implemented are just as important. I think that you would get a lot more satisfaction from a newer player with a better transport and a non-oversampling DAC. 
A used Audio Note would be great, or a reliable transport and an Audio Note Kits DAC. 

"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.
with the CD6007 released, prices are good on the CD6006 and it should way outperform your CD40...I always found the expensive Sony DVD players to make lousy CD transports...
Good to hear that the modern Marantz should be better. This will make me less hesitant to upgrade.
Although I own a Marantz hdcd-1, I also have an Audiolab cdt6000 transport. I use a Border Patrol Dac. Good combo.
I would make sure it has digital outs. If it has RCA/Coax even better. I like the idea of you adding a DAC later on. R2R like the Denifrips Ares II is better on SS gear. If you are running tube gear a chip based system would’ve better. Like the Topping DAC.  Apollo has reliability issues. The NAD is built like a tank and sounds like a traditional CD player. The BADA is nice but I don’t know about reliability. Marantz/ Denon product sound a little warm. If you are running tube gear get the NAD. If you are running SS get the Marantz. This way you will balance the sound a little. Get a 14- 12 gauge power cable for the CD player. It will add weight to the sound even if it is a cheaper Amazon or Chinese cable. If you can swing the $240 go with the Puritan Classic Plus power cable. It mellows out that digital sound and adds sound stage and decay to the sound. Or should I say it lets the music play as it should.  I also like to use Puritan power cables on streamers  like a Sonos or BlueSound and DACs. Good luck and I hope this helped. 
If the Marantz is in good shape and you know the seller I would purchase it and save the $$.
Here's my two cents:  first off, there is no substitute for critical listening or auditioning equipment under controlled circumstances.  That being said, seven years ago, a Sony CD player that was gifted to me died.  So, I did my usual research & reading and went out to do some critical listening under controlled conditions.  I listened to a Marantz CD6005, its direct NAD competitor in the same relative price point and an NAD player that was about $150 above the Marantz's price.  I didn't have to listen very long to either NAD.  I bought the Marantz.  For my tastes, the NAD units were very flat in frequency response.  So flat, that neither of them were nearly as musical and dynamic as the Marantz.  I haven't heard the newer NAD players.  So, I have no idea if this sound signature has changed.  If you read reviews of players you will find that Marantz consistently outperforms almost everything in their respective price points, year after year.

My friend recently purchased a factory refurbished Marantz CD6006, largely because of how much he liked my CD6005.  He is very happy with that decision.  With the CD6005, I started with the conventional RCA analog hook-up and, then, switched to "AUDIO EX 2" mode.  Very easy; done with the remote and a couple pushes of a button.  This was a slight but immediately noticeable improvement in sonic performance.  I now have it connected via Pangea digital coaxial cable, using it as a transport with the DAC in a McIntosh MA5200 integrated.  I'm still trying to decide if this is an improvement over "AUDIO EX 2" mode.  My immediate take is:  maybe an extremely small increase or improvement in bass response but I need to listen more.  Maybe the DAC in the MAC needs more burn in time because this is the first time I've used it.  My friend has his CD6006 hooked up via digital coaxial to his Pioneer Elite AVR and he absolutely loves that player.

I'm not familiar with your amp.  If it has a quality built-in DAC you may want to consider a transport, as opposed to a player.  Here are 2 in your budget range that I've read good reviews of that you may want to consider:  Cambridge Audio CXCv2 and the Audiolab CDT.

Good Luck!
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 !
Get a pro grade CD player like a Tascam from Musicians Friend and run a digital line to the DAC of your choice.  There are some very good DACs on the used market that offer excellent value.
I think you should try to find a good vintage cd player prior to 2000 like an adcom gcd 750 or a wadia or an accuphase they will all sound better in many ways than what you are looking at right now.
I'm still using a 1986 Denon 1500 and still sounds great!  I have friends with newer CD players, only one can match the sound, most can't compare.  I attribute this to 1500's Brown and Burr DACs !! 
I’m still using a 1986 Denon 1500 and still sounds great! I have friends with newer CD players, only one can match the sound, most can’t compare. I attribute this to 1500’s Brown and Burr DACs !!
I am sure the Denon must be very good. I learnt something new about this player when I googled for this Denon 1500: https://forums.stevehoffman.tv/threads/a-legendary-classic-the-denon-dcd-1500.214154/

Looking at the pictures of its internal circuitries and parts , I don’t think the Marantz CD40 is as good, components wise.