Marantz NR1504 is meant for passive speakers. I have the same situation as yourself, using old 5.1 amplifier (mine is Sony amp) driving genelecs with RCA-XLR cables. So I updated to this pre-amp: https://www.hifikulma.fi/Rotel-RC-1570
I have tried both RCA and balanced (XLR) connections with 8320A speakers and I won't be using non-balanced connection again. However my source is a computer soundcard that already has balanced output available. With this setup the balanced connection is more dynamic and there is 0 background noise from the computer electronics such as the graphics card.
I suggest you look at pre-amps. Many good old and new models are available with "impedance balanced" output. This is not the same as fully balanced construction through the whole circuit board, if you want that kind of preamp then you need to spend about double the money (for example Classe audio). Also I have read that many people have good success with Apogee Duet interface with Mac and this is a "cheap" way to get good quality balanced audio. I don't believe any computer interfaces offer fully balanced construction throughout the circuit board.
With some Cambridge Audio streamers you can get AES/EBU output and also they have received good reviews and these can be bought a little bit used for under 1000€ so these might be a good option if you like that brand. That way you can keep digital signal all the way up to the speaker.
in case you don't have analog sources, don't use analog preamps.
drive the speakers digitally, whichever way, and use GLM + 9101AM for volume control.