Balanced Interconnect Recommendations

If the circuit topology of your components are not fully differentially balanced from input to output then there is zero sonic benefit of using balanced ICs.  In fact you could even make the sound worse in some applications such as taking a balanced signal from a CD and sending through an unbalanced amp which creates unnecessary conversions that may degrade sonics. 

But if you take a balanced signal and connect it to a preamplifier that is truly balanced - it keeps the signal balanced from input to output, then the preamplifier’s balanced output can then be connected with balanced cables to a power amplifier, whose input circuitry is also balanced. In this case using balanced connections has theoretical advantages over unbalanced connections. These include the benefits (in theory) of lower noise and randomization of DAC non-linearity plus balanced connection noise immunity.  Whether you notice the difference varies from system to system and person to person.  

@almarg   So your contention is that the benefit of common-mode rejection inherent to an XLR connection may provide an advantage over single-ended connections in some cases?  I'm not sure common-mode rejection is the most important factor to be weighing when selecting cables but I can't disagree with you 100% either (only 99.9% ;-)).  For instance if you're talking about a short length and a low-gain signal then a single-ended circuit may very well outperform balanced regardless of common-mode rejection.  This discussion feels more theoretical than practical and it sounds like we both agree that the vast majority of the time the user is much better off in terms of both cost and performance to only go with XLR when engaged with  fully balanced circuit.  And agreed, if you don't mind spending the money and investing the time, sure it never hurts to try both ways.  I just think there are higher odds pursuits to improve audio quality.

@almarg   The reason that balanced lines are going to be more resistant to noise is due to common-mode rejection so I assumed (incorrectly) that's what was underlying your points.  And yes, you referred to common mode rejection exactly in the way I meant as well.

Perhaps someone(s) on this forum who is using unbalanced circuits could do a comparison with RCA vs XLR IC to see if it makes a sound quality improvement in their system. My main system is fully balanced from input to output and I use XLR's only due to that topology.  My second system uses an integrated amp...otherwise I'd volunteer!

The Isis is fully balanced though correct?