There are several methods of balancing a line; one of them involves impedance balancing, which still cancels out any induced noise when inverted, but the second line (pin 3) doesn't carry any audio signal. You don't get the 6dB boost from inverting.
Keep in mind this one simple fact: When your "balanced" signal goes into any of your rack boxes, it's immediately converted to an unbalanced signal for processing.
If there's also a balanced output on the box, it means there's also an extra stage, converting the now unbalanced signal back into a balanced signal.
So, your carefully balanced signal goes thru two additional stages in those boxes; one active stage to invert, combine, and unbalance the signal (so the box can do whatever it's gonna do to the signal), and a second active section to balance it again to make the trip out of the box - to the next box, where these additional i/o stages are repeated.
If your mic is plugged into a mic preamp, then a compressor, and maybe an eq, that's five additional conversion stages that aren't really needed - all they're doing is unbalancing and balancing the signal, over and over.
If all the equipment is reasonably close to each other, and you can run short cords, unbalanced routing actually wins over balanced. You should use balanced lines for long, low impedance runs, or when induced noise and hum may be a problem. For short runs to (and between) outboard gear, why add unneeded stages that can degrade your signal?
Don't take my word for it; try it yourself. Take the unbalanced output from your mic pre and run it unbalanced all the way to the recorder, thru any effects you want. Then take the same chain; use the balanced ins and outs, and listen to the difference. You tell me what you hear.
) Do I need balanced cable from mic to preamp, and then 1/4 TRS cable from preamp to PC? And...Do I need new soundcard, because my soundcard doesn`t have 1/4 input... Pease help 
