Balanced vs RCA between amp/preamp

the sound of the interconnect won't be a thing

Malarkey!

Assuming balanced circuitry and connections are properly implemented, which far too often they are not, they can reduce common mode noise. FULL STOP.

For balanced interconnects to be immune to cable, they would have to be immune to the laws of physics. Balanced lines [and connectors] have impedance and impedance controls frequency response.

differential amps tend to be lower noise we don't need as much gain stages to get the job done

If number of stages is a criteria, use a transformer. Differential amps per se are all over the map in terms of gain vs noise. The devil is in the details.

the other reason for balanced lines is elimination of ground loop noise

I'll wager that 6 9's of 'balanced' home audiophile systems do not lift the shield at the destination. Depending on amplifier design, there may be ZERO ground loop improvement over an unbalanced system.

The balanced line system was created to get rid of interconnect cable colorations

The balanced line system was invented by the telephone company to increase noise immunity and power transfer over long distances. Nominally 600Ω, but at 1 frequency ONLY! Low frequency performance is abysmal.The 'telephone sound' is a direct result of balanced cables.

Sorry, but posts like the above are just fanboy prattle, equivalent to
      "I changed everything and it sounded different."

Many balanced devices are bodged to accommodate unbalanced operation and coupled with generally incorrect balanced wiring, they don't stand a snowballs chance of optimum operation in unbalanced mode.

If 4+ decades in electronics has taught me anything, it's that if it can be screwed up it will be: 

• inexperienced engineers
• incompetent sales staff
• ignorant consumers
  

Hi Al,

I should have said "Use caution if driving an unbalanced amplifier from the balanced outputs."

Thanks for catching.

- Best,
    Ian

for anyone interested, HDAM module schematics are available here https://muzgdiy.files.wordpress.com/2015/05/all_versions_2.png

These HDAM's consists of discrete surface mount components with short mirror image L/R signal paths.

IMO, this is marketing malarkey. It is not possible to 'mirror image' active circuitry as devices have functions on specific pins. Marantz literature always shows a pair of identical HDAM modules and never a mirrored L/R pair which, if they existed, would be featured front and center. Additionally the Service Manual has only one HDAM-SA3 schematic for a bipolar amplifier circuit.

Discrete circuity 'suffers' from increased parasitic L & C, component tolerance and reduced supply immunity, all of which contribute to the 'sound'. Some opine that discrete circuitry takes the edge off the literally 1000's of integrated circuits through which the signal passed before the final storage medium.

Somewhat troubling is the -ve phase is derived from the post Wolfson WM8816 volume control unbalanced +ve output through an additional 2 HDAM and 2 gain stages. These then feed a pair of balanced tone control circuits. Strange.

Use caution if driving an unbalanced amplifier. Best results will probably result from using Pin 3 & Gnd ONLY.

A largely ignored electronics property is power supply linearity. The impedance and phase linearity of the ubiquitous LM3x7 / 7xM  et al. regulators vary drastically between manufacturers and implementation. Some are positively abysmal suffering 180° phase and a couple of orders of magnitude Z change in a few Hz.

Marantz makes a fair bit of 'noise' about their power supply design and examination of the schematic shows that the audio supply is discrete and well designed.

A negative in the pre-amp [and any versatile control center] is the large number of relays in the circuitry. ALL switching is audible and cumulative.

Bottom line, if you like the sound, don't worry about the innards.

PS I have a Marantz CD-6006. I like the sound & features. I don't worry about the innards.

In a balanced line system there is no need to lift the ground at one end of the cable. 

Try not doing it in a large multi-room facility like a sound stage, dubbing room. It may not be required with the AES-48, but until all gear is to that standard, prudence takes precedence over valor.

Most XLR gear is not transformer coupled. Not all is actually balanced.

In transformer gear, an unbalanced signal is fed through the transformer. The output can be XLR, banana, TRS, multipin, etc., etc.

While the Jensen transformers are excellent, they, like all transformers, still have a sonic signature.

Depending on the issue, adding transformers with the screen carried may not solve the problem.

The way to solve a ground loop is to purchase properly or fix improperly designed equipment. Adding a transformer is a bandaid. Bandaids fall off.

My company wired recording and film studios in Los Angeles and New York in the 1980s & 1990s. We had transformer and electronic balanced and unbalanced equipment to interface. Hundreds of connections that could be reconfigured into literally millions of combinations. Correctly done, there is no ground loop.

If you detail out your equipment and connections, perhaps we can solve your issue. By detail, I mean brand, connection, electrical power etc. Since we can now post images, draw a sketch.