How to accomodate a balanced only phono stage ?

Hope this doesn't go down too badly as my first post!
and I was just about to post about getting a new cartridge.

I don't think it is as simple as that.

The problem with running balanced from a cartridge is that the input electronics are doubled which creates 'electronic' noise and not 'common noise' which balancing cancels (CMRR). Common noise in a turntable cartridge system should be nothing significant if your system is setup correctly. Input stage noise though, due to doubling of stages/ components creates more problems than it can solve.

If you have noise or hum from your turntable it is better to look at 'why' than to try and irradicate it using balancing..... prevention is better than cure!

From what I can see, it is a marketing ploy by some phono stage manufacturers, and usually the not so serious ones, and seems to be the fashion for now... I have listen to it and am not at all convinced it is worth the effort and if anything looses some of the 'air' and speed that the single-ended RCA connection gives.

I think to be truly differential it needs a center-tap 0v.
MC cartridges do not have a center tap so the ground (0v) is floating and does not form part of the signal. The ground path of the tonearm should not be part of the balanced signal - pin 1. The chassis is normally pin 1 with 2 hot and 3 cold OR pin 1 CT (center tap), 2+, 3-.

A mains transformer has a center tap for the 0v which the preamp or amplifier uses as the 0 volt reference and is used as the 0 volt reference for the system.

I don't think anyone produces a Moving coil cartridge which is truly balanced - having a center tap. This would mean having 6 pins.

Just keep in mind that the typical "RCA" cable will have only one conductor for the signal. The "ground" connection in an RCA-terminated cable will typically be carried on the shield that surrounds the "hot" wire. In balanced configuration, there is no "ground". The "hot" wire of an RCA cable fed a balanced signal will carry only the positive half of the signal, and the negative half of the signal will travel on the shield of the cable to the outer ground connection at the RCA plug. Even if you use RCA to XLR adapters, this is the case. Some contend this degrades the signal. Better, IMO, to do a little soldering and change over to XLR, 3-conductor cables all the way.