Is there advantage to balanced phono-preamp

Whether it's a moving coil type or a moving magnet type or any of the variants thereof, the signal comes off a coil of wire.  At either end of the coil, the signal looks the same, except for its being opposite in phase.  So, a cartridge is an inherently balanced output device.  When you run it into a typical standard single-ended phono stage, you make an arbitrary choice to take the signal off one end of the coil and to ground the other end.  But there is no need to connect to ground.  In balanced mode, you just connect the coil to another identical circuit.  Because the two signals are 180 degrees out of phase, any noise common to both signals is cancelled.  You get a bit more gain in balanced mode and that advantage of noise cancellation, known as Common Mode Rejection.
Brrgrr, usually you won't want an XLR to XLR phono cable. Usually you will want a DIN to XLR cable, to connect your cartridge to a balanced phono input.  Yes, they are made, can often be custom-made too.

CLeeds, Please note that I used the word "usually" when describing the cable needed.  You've pointed out the cases where one would do other than the usual.  I was trying not to overwhelm Brrgrr with details. Thanks.

You wrote, "For example, some balanced phono preamps use RCA connectors on the inputs and a ground wire separate from the signal’s neutral. ARC phono preamps work this way and as long as you keep the shield electrically separate from the neutral, you’ve maintained the integrity of the balanced connection."

The user should beware of using an RCA-terminated IC for balanced phono, since in that case it is possible that one half of the signal, which for convenience we can call the negative phase, is being carried on the cable shield.  (There is no "neutral" in the balanced mode.) That is a compromise I would not care to make.  If the cable is knowingly constructed for balanced operation using RCA terminations, then the maker can use two conductors of equal quality for each "half" of the signal, one going to the central pin and the other going to the collar normally used as ground.  But inside the phono stage, that collar must be connected to the circuit that amplifies and RIAA equalizes the negative phase, not to chassis ground.  (Does ARC do this?) Otherwise, you don't have balanced operation.  Any ground wire is just to keep the phono stage/tonearm/turntable at the same electrical ground point.  It can be completely external to the cable itself, as I think you say. In balanced mode, audio ground can float.

Are you sure that ARC phono stages that purport to be truly balanced use RCA input jacks? (I've never seen one in the flesh, much less owned one.)  Seems to me they ought to at least offer the option of XLR input, along with RCA.  I can see why they might provide an RCA option, since most phono cables are RCA-terminated, and since most audiophiles are hopelessly confused about balanced operation.  Every other true balanced phono stage I know about provides XLR inputs, plus or minus RCA inputs.

I owned an Ayre P5Xe-mp, and selling it was a mistake.  It was great as a spare and as a second phono stage for MM/MI.  So, I second your nomination.