RCA to XLR adapter, advantages of special boxes ??

Your signal from the CDP is a single-ended signal. In order to get a differential signal for the AES/EBU specification, you need two signals, one non-inverted and one inverted. The box that you speak of generates these two differential signals from a single digital signal. The differential signal will give you more noise immunity and probably less jitter as well.

I want to thank you all 3 guys that helpend with good advises. Few more info as a feedback for your courtesy:
the DA converter is a professional one used in recording studios, this is the reason it has XLR plugs.(believe me much better that hi-pricey DAC often sold at hi-end)
Unfortunately, but with a future upgrade this could be improved, my CD player has only two possible output:
S/PDIF coaxial RCA or Toslink lightpipe. This is why I need to take the single ended from the CD and plug it into the DA converter.

At the same time the DA converter has XLR output and as usual my preamplifier has a simple RCA input !

Yes, JAX2 I realized I will lost the balanced advantages, but as said, with a future upgrade..........

Tks to anybody so far

The kind of adapter differs from regular analog RCA-to-XLR adapter because S/PDIF & AES/EBU have different communication protocols. The DAC won't recognize the S/PDIF protocol riding on AES/EBU connector if you use analog RCA-to-XLR from BAT or Cardas.

Agree with the posters who point out the difference not just in the connectors, but between the S/PDIF (RCA) and AES/EBU (XLR) signals. One of the best ways you could accomodate this connection, IMO, is to buy a new or used Monarchy Audio DIP jitter-reduction box (these are a steal at about $250 new, and sometimes less than half that used, with the latest and supposedly best version being designated "24/96", but any of the iterations should work fine). It will accept Toslink or RCA S/PDIF inputs, and output a cleaned-up and reclocked balanced AES/EBU signal on XLR. In addition to its very effective jitter reduction properties, it is also features transformer-coupling on both its digital inputs and outputs, electrically isolating your converter from your transport's or computer's ground-plane noise.

WOW, discussion became hot ! I really appreciate your help.
Question: if I shall invest some money, for that Monarchy box, wouldn't be better to invest it in a new CD player with AES/EBU output ??
Which prices ??
I could sell my actual one (DPA Enlightnement) that has already 5 years of operation !
What do you think about ??
Which budget should I afford for a decent cd player?It might be that 500 USD will beat already my DPA, isn'T ??