there are two ways to turn an unbalanced signal into a balanced one.
1) PASSIVE: you can use a transformer (put "hot" on one side of primary, ground the other side. the secondary now spits out a differential output.) when you see "transformer balanced output" listed on a piece of gear's spec sheet, this is what they're talking about. in all reality, you might like what the transformer does to the sound. transformers play a huge part in why some of our favorite gear sounds the way it does (read: 1176, LA2A, Neve pres). if you decided to go this route, the quality of the transformer is ***CRITICAL***. don't expect to pay less than $100 each for jensen or lundahl--both quality transformers. you also have to specify the type of transformer you need, as if you're running line level through what is considered a mic transformer, you'll saturate the core and get distortion. lots of things to keep in mind here.
2) ACTIVE: by using opamps, transistors, tubes, etc. (there are several different designs) you can gain a balanced output. however, audio is running through this curcuit, so component choice, design, etc. are certainly a factor is how well the circuit works. the advantage of an active design over a passive one is that the electronics are a fraction of the cost. the down side? if you're doing this at home, you'll need electronics knowledge.
unless you're using all 30 of those line-level sources at once, you might look into buying a pair of passives, and a pair of actives, and just move them around as you track the different sources, that would also give you different flavors for different situations (transformer v. active). (also, i only say "pair" because i'm thinking of stereo sources, like a piano or string patch.)
sorry for writing a novel,
"My job is to make music sound great and to not whine too much." --George Massenburg