Here is a good solution for portability. completely autonomous: the Roland KC110.
- Runs on eight AA batteries, eight AA rechargeable batteries, or AC power (adaptor included)
- Highly efficient 30 watts (15W+15W) stereo amplifier with two 6.5" (16 cm) speakers and two tweeters
- stereo digital effects built in: reverb, chorus, “Wide” chorus, and EQ; effects on/off can be controlled with optional footswitch
- Three independent channels with volume control
- XLR Mic/Instrument input, two stereo inputs, stereo AUX input, stereo line outputs, and headphone output
- Built-in tilt-back stand
- Removable battery cartridge for easy battery replacement
So you can have a theremin with his Kaoss Pad for stereo effects, then you can add some voice, guitar ...
You can even use it as monitor on stage!