balanced connection, better than single ended?

If you have gear that can do balanced & unbalanced connections which is preferable and why? I have read that balanced connections are better for long runs of cable otherwise a single ended connections are fine but not sure of this since I have yet to use this sort of connection. Also I read that some gear is not truly balanced in their circuitry thus this gear may not benefit from a balanced connection. I ask only because I'm recently buying an amp that has true balanced circuitry but now must find a preamp of the same.
Rwwear, I wonder if that increase of 6db of volume is sometimes perceived as better sound quality?
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Balanced or Symmetrical power is explained quite well here:
A true balanced line interconnection circuit needs to be present in both of the devices being connected in order to realize any advantage.

For many years balanced line connections were mostly used in professional applications where long cable runs were common. In a recording studio or public sound system environment, cable runs of 75', 100' or more are not uncommon. A balanced line has a much better common mode rejection of extraneous noise, so will be much quieter (less hum, hiss & other interference pickup) with long cable runs.

Balanced interconnects have become a popular option on some higher end home equipment. The trade off is the use of transformers or differential circuits which complicates things a bit. Whether this extra circuitry is worth it or not is something only a buyer can answer for himself.

You are also right there are some pieces of equipment that offer XLR interconnects but do not have true balanced circuits.

Keep in mind there are many other aspects of electronic equipment design that may make a bigger difference than this one issue. In other words, if you use typically short 1 or 2 meter interconnects commonly seen in home stereo use and hear a difference between two components, it may well be due to a factor other than a balanced vs single ended line.

My two cents is don't get caught up with this one issue. If you audition two pieces of equipment and prefer one over another, don't waste too much time worrying about assigning a reason to a particular technical detail.
>>> I ask only because I'm recently buying an amp that has true balanced circuitry but now must find a preamp of the same.

If you can find a "fully" balanced pre that you're happy with, that's great but I wouldn't limit myself to that only. I have a balanced amp and drove it with a balance preamp. Life was good. One day I demoed a preamp that only had rca's and it was much better than the balanced one.

Find the best preamp for your budget and don't worry if it's balanced or not. Go by the sound.