"My band uses a '16 channel' Mackie mixer at our live gigs. I say '16 channel' because it's really 12 channels with two stereo line input channels for 16 total inputs. We already use all 12 channels, but I just added a second keyboard to my rig and would like to use one of those stereo line input channels in the front mix rather than buying another mixer to submix on stage. We do have a 16 channel snake, but I've been told I can't just use adapters to run my low level keyboard through the 100' snake. I use a direct box on my other keyboard, but the level is too low when I put that signal into those line inputs. What can I do?"
Anytime you are going to send a low level (as in line or mic level) audio signal a long distance like this it really needs to be balanced. Of course this is one of the things accomplished by a direct box, but then those signals are low level and intended for a mic preamp, not a line level input. Fortunately those stereo line inputs on your Mackie are balanced inputs. That may or may not be true of other mixers, but this trick depends on it.
The output of your keyboard should be hot enough to drive those line inputs. We just need to make it a balanced signal without lowering the level like a direct box does. You can accomplish this type of thing with resistors or transformers (not to mention any of a number of active devices). A great way to do this with resistors is detailed in the Tech Tip from 11/26/99. Transformers work well also, but the specific wiring will depend on the exact transformer you get. If you know how to do this you probably don't need this tech tip anyway. There is a great off the shelf solution for those who don't want to build stuff.
A company called Ebtech makes a handy little box (LLS2) that employs transformers to change signals from unbalanced -10 dBV levels to balanced +4 dBu levels (see our Summit on +4/-10 for more than you ever wanted to know about that topic) and is normally used to interface such equipment together. Though you don't really need to increase the level of your keyboard in your situation it will not hurt to have the level boosted. The real benefit of this device in your case is in balancing the signal. Use a cable or adapter to change the male XLR end of your snake at the mixer into a balanced TRS connector and plug that right into those line inputs on the Mackie. The signal from the keyboard will be hot, but not too hot, and you can always turn it down at the keyboard. The LLS2 is a two-channel unit that works great and it doesn't cost more than a couple of decent direct boxes. There are other more sophisticated and expensive devices that will do this, but we're assuming you're operating on a budget here.
