That's the key.
Some amps with balanced input need more than 2V to reach full output power (e.g., Topping LA90 Discrete).
Moreover, some amps have different gain settings - the lower gain settings have a better SNR. Balanced output, at double the outp okut voltage than unbalanced, may allow for a lower gain setting. E.g., in the middle gain setting (21.8) with 4V input, a Hypex Nilai amp will output as much power as a 2V input in the high gain setting (27.8), but with 5 dB better SNR (109 vs 104).
Also, with my Nilai, the mid gain setting is fine with 4V input, but after I apply a lot of PEQ in DSP, it works better with high gain. 2V input would would be too low to get near full power with the DSP I have applied.
Personally, I would not use an RCA to XLR cable for the reasons discussed above.