Adding XLR adapters will make matters worse. The audio signal will just have to travel through another device. The beneficial feature of XLR connectors is that they are used on balanced cables, which you don't have, and can't have, in your system as described.
Just a thought here but,,,,,,xlr adapters?
My OPPO UDP205 used as a DAC has XLR output sockets. the rca outputs are currently being used.
My Revox B-77 has RCA inputs and outputs.
My pre-amp Audio Research SP-9 MK III, RCA inputs
Recording speed, 7 1/2 ips. 10 inch reels.
I was thinking of XLR adapters for the Revox's input / output to help with tape noise not so much from the dac but to the pre amp.
Any thoughts? suggestions? constructive criticisms?