line level is -10dBV
balanced is +4 dBu
I don't realy understand this voltage stuff, but a balanced signal is dubbled at the target since the cable runs normal and an inverted signal which will be summed (that's how the noise cancels out)
That's a myth that still seems to be prevalent. There is no doubling on a balanced signal, a balanced, or a better term is 'differential' signal just has two legs that have voltages of opposite polarity
with respect to each other. Whether that's double a single-ended voltage is only apparent when trying to unbalance a balanced and differential line. If it's centre-tapped, i.e. earth referenced, then it can be simply unbalanced by going between either leg and ground, ignoring the other leg. That will result in an unbalanced signal half the size. However, if it's a fully-floating balanced differential line, whether transformer or electronically balanced, then either leg can be grounded and the signal taken from the other leg, in which case there is no halving of signal.
It's necessary to know what sort of balanced differential output one has to know the best way of getting a single-ended output as earthing one side of a centre-tapped (earth referenced) output will short out one side, which at best will most likely increase distortion and at worse damage the output driver.
I won't even go to impedance balanced single ended outputs!
Going the other way, from a single-ended source to a balanced differential input is very easy, just go between XLR pins 2 for signal and 1-3 strapped together for ground. If there's a hum loop created, try removing the link between pins 1 and 3, leaving pin 1 floating.
S.