I stumbled upon your post after pondering already a couple of weeks about a configuration for a phono stage. Indeed there are not many advantages for a balanced phono input. AND compared to a true single ended input, with a differential input (necessary to go balanced) one pays a penalty of twice as much equivalent input noise. And more parts of course (= €). But hey, don't we want to hear what's on the discs?
Anyway I have been thinking, and I knew five balanced stages (by heart) when I saw your remark that no five had been mentioned yet. They are:Vacuum State Electronics RTP3, Einstein "the turntables choice (Bal option)", Borbely EB 804, EAR 834P and Manley Steelhead. The latter two are pure tube, and there many truely balanced inputs for phono inputs can be found: a step-up transformer is very nice for balancing! However the impednce of the primary is effectively in series wit the cartridge, so you pay a penalty noise-wise. Noise pick-up by the lines can be a lot less when using balanced interconnects.
The guys struggling with balanced from a single generator (the cartridge) may try imagining this: The generator at the far end of the tonearm really does not care what wires are connected to its exit pins... It just translates lateral needle speed into voltage. Now if the + and - both have the same impedance to ground, we have a balanced line. this means that (stray?) capacitance, inductance and resistance are alle equal toward ground for the two conductors carying the signal. Whoopps... What the heck?? In practice: if you use a twisted pair inside a grounded (but nowhere electrically connected!) shield you have a balanced line. Have a look at good microphone cable. and dissect a piece. Now follows automatically that the 'normal' coaxial wire often used can never transport truly balanced signals.
Well, is it worth it? I conclude yes: getting rid of the coax and installing a balanced interconnect on a turntable gives advantages most of the time, even with a single ended phono input.
Is a balanced input on the amp worth it? Well, ehh, it depends. sometimes it gives a very elegant solution to biasing problems (e.g. as in mentioned VSE RTP3). something like this is what I will build.
just some thoughts... cheers and enjoy the music!!