The PMB-1 would work very well for this purpose. I have one that I've used for mixing the 2 outputs of my Chapman Stick, which require different EQ and gain settings. The effects blend control is very useful and the mute and phase reversal switches have come in handy.
Plus it's extremely quiet, has uncolored studio-quality sound, and can be battery powered. With the channel and master gains maxed it has enough signal to drive a power amp on its own, but it's more suited for mixing instrument-level signals into the front of an amp.
That said, I'm planning on selling mine because I need a preamp for the Stick with separate XLR channel outs, headphone amp, and more powerful EQ. Mine is in mint condition except for a couple minor scratches-I 've only used it for a total of maybe 6 hours at home. Please email me privately if you're interested.