Today I was talking about doing exactly that.... the best way to upgrade the tant cap is to *replace* that tant cap. The 4.7 uF Wima may be a perfect candidate, although technically having a lower coupling value may result in early LF rolloff if the CDP is used into a preamp with a lowish input impedence.
Then simply parallel two 4.7uF Wima's as your base capacitor.
Another idea;
Given that you'd prefer to use all Cardas, but don't have enough space within the CDS3, why not simply bypass the Tants and fit your Cardas cap's in a suitably sized external 'coupling cap' box. In fact, an external box would mean you can very easily experiment with various combinations of capacitor without the PITA it must be to delve inside the CDS3 for every change. You might hit on something that sounds great and yet is small enough to be housed back in the CDS3.
Mr Tibbs