Better cd SQ

I've got a Marantz SA 8005 CD/SACD player. It's very nice and has the guts (DAC chip, etc.) to sound fine. But...I picked up a PS Audio UltraLink DAC at an estate sale for $25 (yes, that's right), and, well.... Admittedly, the UltraLink is very slightly louder than the Marantz; also, the UltraLink won't play DSD, so I listen to SACDs through the Marantz' internal DAC. But I can switch between the Marantz and the UltraLink with the remote to A/B compare them on Red Book CDs, and I always prefer the sound of the UltraLink. It's hard to describe the difference; the UltraLink just sounds more like live instruments, less like "reproduced" music. But, again, there's nothing wrong with the SQ coming from the Marantz. So, yeah; a stand-alone DAC can up your game in subtle but compelling ways.

Addendum to the PS Audio UltraLink note above. Robert Harley, in Stereophile, loved this DAC. His "Conclusion" begins like this: "The PS Audio UltraLink offers many aspects of high-end digital processor performance at an unprecedented price. The product's soundstage transparency, focus, sense of air, and palpability have not been equaled at this price level, in my experience. Indeed, the UltraLink rivaled the $14,000 Mark Levinson No. 30 in these areas. Moreover, the UltraLink's resolution of transient leading edges and dynamics were superb by any measure. The overall presentation had much more in common with state-of-the-art digital processors than with comparably priced competitors." 

However, this review dates from 1992! I've read several testimonies in this forum that remark on how much better DACs have got in recent years. If that's so, and the 32 year old UltraLink still sounds unambiguously better than a higher-end and fairly recent Marantz SACD player...well, the implication is that the OP would be wise to do what he's considering doing.

I just purchased a Denefrips Pontus ll. It's still settling in but it's a treat so far. 

Remember this if a CD is not done well it won't make silk out of a sows ear. A good CD sounds wonderful 👍

Forgot to mention a used Weiss Dac would be a great option if you could swing it!

I have the CD6006, also had the 30n SACD...I wouldn't go much above a Denafrips Ares 12-i or Schiit Bifrost 64/2...above that I would get a better CD Player or separate transport and DAC...the Marantz 30n SACD sounds better than the CD6006 if you like the Marantz sound, and also offers streaming...