Advantage of Balanced over RCA for phono cables

This is not the answer you are looking for because it's vague however in my opinion you have to try it for yourself, in your own system, to really know what you prefer. That's not an inexpensive thing to do unless you have some friends or a dealer that can loan you some balanced cables.

Kurt is correct . . . except for some very rare instances, a phono cartridge is always wired as a balanced connection - it can be thought of as a transformer with a mechanical (rather than electrical) primary. And given the ratio of a cartridge's common-mode versus differential-mode source impedance, the interconnection to the preamp can retain most of the noise-rejection performance of a balanced line even if it's terminated to an unbalanced input.

There's very little performance difference that's associated with the XLR-vs.-RCA connectors themselves as they're the same connections . . . for conventional RCAs, the separate ground wire is used in place of pin 1 on the XLR, and the tip and ring of the RCA correspond to pins 2 and 3 respectively (American standard; European standard reverses pins 2 and 3).

For the cable to the turntable, using shielded-twisted-pair construction helps preserve the impedance balance, and thus improves immunity to magnetically-induced hum. The tradeoff is higher capacitance, and for MM cartridges this can be a problem . . . so personally, I prefer simple coaxial phono cables of as short as practical for MMs, and shielded-twisted-pair for low-output MCs.

For the phono stage, so much of it is the designer's preferences for the particular topology, and whether or not it lends itself to a balanced input . . . because the balanced nature of the cartridge can make the noise rejection similar between the two. One can't escape the fact that an active balanced differential input generally a minimum of 3dB noisier than an unbalanced input, but whether this ends up being significant in the context of the entire circuit is another matter.

I think you better touch base with Aesthetix. The Io has a single ended input stage and then balanced output stage. So, only a guess, is rca input cable is fine...balanced output