MIDI is right, an analog mixer might be a good first step. You might consider the PEAVEY PV20 USB which lists for $499 at Sweetwater. It has 20 input channels total including 16 Line/XLR (i.e., microphone inputs with preamps) and 2 sets of stereo inputs as well. It also has quite a few special effects and a USB connection where you can send the live audio mix to your PC for processing and recording. Each input channel has a 3 band equalizer, balance, and gain controls which you can use to set each instrument/vocal level independently. I use it in my home studio for producing "cheap" live demos since it can handle 5 drum mikes, bass input, guitar input, 2 keyboards via the 2 stereo inputs, 2 Leslie mikes, and still handle several vocal mikes. Just remember, it's not a DAW so you can't post-process individual tracks but you can capture the whole band in a single session. Hope this helps and good luck.