Matching fully balanced with unbalanced.

In my experience only listening will really tell, as it also depends *how* the balanced is IMPLEMENTED in the source equipment(s). 

This unless some very long IC connections will be the case and RF issues adding to the mix. 

With my equipment (all ML) feeding PASS poweramp, and having tried unbalance, balanced *always* by tiny SQ improvement won the day.
This, mind you, with no IC longer than 5' and the shortest less than 1'.

At the same time folk with diffent equipment and set up, having different synergys, will tell you, unbalanced will improve air and spaciousness, as oppose to a more dence and firmly focused image presentation.

Long story short, only testing and listening will tell it, is my learning.
Michélle 

Of course testing and listening that for sure, but could any body throw scientific base under this topic?

I prefer the single outs/ins on my system. Long cable runs are not an issue for me, and really the primary reason to run the “balanced” outs/ins is mostly this. Also, as mentioned, few systems are truly “balanced” anyway...

Not sure the science of your question was not answered already...? 
If *balanced* is 'pseudo balanced' i.e. achieved by opamp implementation as compared to 'fully balanced' implemented by two seperate strands of amplification within one source unit, the notion is that fully balanced is superior technically to a 'quick fix' opamp implementation. 
So, if the equipment is not a fully balanced design (looking at the design diagram was already mentiond) THAN it will by deduction appear to keep the opamp out of the source line AND USE THE SE (single ended) connection. 
Drilling further into the science of whether the addition of on opamp is beneficial to sound quality can be answered by listening, what has been mentioned. 
BTW, that opamp chops a full audio sign-wave into a negative and a positive, so it's up to the beholder to decide whether this is of no import to the signal further passed down the line. 
Again, if the final stage the poweramp has a pseudo balanced input option, the use of this also involves an opamp to first combine the two halve waves, ahead of the actual poweramplification stage(s). 
Common sense, at least, suggests that this again will not lead to any signal improvement but rather to a degree of its deterioration. 

Not sure this fully will answer the question regards any scientific proof etc.. 
To do THAT, a signal analyser would need to be called for plus engineering experience in explaining the results generated. 
M. 

surfmuz OP7 posts05-23-2020 3:45pmOf course testing and listening that for sure, but could any body throw scientific base under this topic?

Sure simple, what comes out of 99.9% of hiend poweramps is SE (single-ended), the speaker terminals are + positive and negative is at ground potential.

Cheers George.