The RCA outputs on the Bartók are by no means a compromise as far as unbalanced outputs go. If the XA25 only has unbalanced inputs, then the performance from the system will be very good provided you aren’t doing anything that really warrants a balanced XLR connection (such as running the cables across the room or past anything electrically noisy). If you have short cables from DAC to amplifier, you should be absolutely fine with unbalanced RCA.
I would also wager that if there was a problem using unbalanced connections in your system, you would have heard the issue with the Lumin going into the XA25. Since you haven’t mentioned encountering any issues like buzzing coming through the system with these two devices, using RCA should be absolutely fine.
As James stated, try a straight RCA connection first. If you really want to take advantage of the XLR outputs of the Bartok/Rossini/Vivaldi and/or need long leads, you could always use XLR transformer-based converters like these https://www.neutrik.com/en/product/na2f-d0b-tx - don’t use simple conversion leads that short pins 1 and 3 to ground.
The RCA output is excellent in its own right and was designed as a state of the art execution. The balanced output has an incrementally better sound (remember this hobby is full of exaggerations). Of course it is feasible that the single ended RCA output may even be preferred by some.
I have tested the two against each other but he current state of play is unclear as the Apex version has a new design. I have not tested it so cannot comment on the level of difference. Therefore it will also depend if you are looking at a new Bartok or a used unit.
Everything else being equal I would be happier with a system using RCA to RCA rather than trying a fudge of XLR to RCA.
The output stage ( after the DAC, before the connecting cable) has been optimised ( to use dCS’ word) in the Apex . You may find this interesting:
I think it worth mentioning that although Apex does improve the performance both judged subjectively and by measurement the previous models of Bartok, Rossini and Vivaldi remain as wonderful DACs - they didn’t degrade overnight
Many thanks for the replies. Indeed interesting read on APEX and how DCS approaches such engineering improvements.
I can call myself part of the community. I today received a (non APEX) Bartok. I am speechless. It is soo damn good (even using RCA). So much clarity compared to my Lumin and at the same time so easy to listen, not harsh at all.
A high investment for my budget. But it will provide me many hours of joy.
