Better cd SQ

I used to have the marantz CD6005. Now have the Jay's CDT2-MK3 with gustard x26 pro. The difference in sound clarity and overall presence is HUGE. I know it's way above your price range, but just making the point that you have lots to gain in moving up from the CD6005. I also used the Cambbridge CXC, better but nowhere the improvement of the Jay's. I hope you will find a way to enjoy your CDs as much as I do. And I run streaming and vinyl too.

+1 for Denafrips Pontus II 12th DAC, about $1,800 at current exchange rates at Vinshine Audio....can be purchased new for a little over $1,800 new with free shipping. Hundreds of positive reviews, sounds more analog than most DACs, US based service center, release updates a couple of times a year, and Alvin Chee at Vinshine is a great guy to deal with.

I've had mine for a couple of years now, and it has remained stellar even though I have upgraded components around it....never thought it was a weak link

A solid Dac choice would be the smart next step. Without knowing exactly what the cirrus chip and output stage of the Marantz may render in tonality and stage characteristics, hard to say exactly what will differ.  It 2k for a dac would get you a jump in quality regardless! Cables do matter, and even digital outputs (and even between dac inputs) can differ in terms of results. But overall, something with a good balance of stage, clarity and spaciousness like a r2r dac would be great. Since you’re running tubes, however…delta sigma might be the right offset? Who knows. 

so many choices, but if you’re not particularly worried about digital input choices and are looking for something kinda special, for around $1700 the ANK DAC 2.1 Signature might be nice with your setup (tried posting a link but got blocked). I think that’s a kit? More to have it assembled. 

That PS audio recommendation would also be really nice with your setup (assuming here). But there are amazing offerings like the Gustard R26, Musician Audio Pegasus II, mentioning these as they are reviewed to hit well about their asking price in terms of tonal balance and performance. But like I said, it doesn’t have to be R2R to be engaging and beautiful, wide and deep while being true to source. I was lucky enough to find a used Okto Research Dac 8 stereo. Most balanced and beautiful dac I’ve ever heard and it’s a very carefully designed ess Sabre implementation. 
 

But good to consider a dac that you can later try with a decent transport since you enjoy the CD format. Yes, there are amazing new all in one’s that can attach an external drive, but I can respect (and prefer) the possibilities with separates. 

"No reason to waste money to play the CDs you have when you can have access to millions of albums at the same or better sound quality."

Such nonsense. 

Amour-all your cd's for a 20% improvement in dynamics....don't laugh.  Try it, you'll like it !