I have a Freebass, currently distorted like this:-

Freebass->Mixer (analogue) Trim gain maxed out, EQ max on all frequencies, this causes distortion on the mixer channel (but you have to be careful and drop down the channel sliders). This is a cheap trick I learned from my Jedi Master!

I put the output level to off on the slider, then I use the pre-send on that channel, throw it through a compressor/limiter, munge it some more then do the same distortion effect with the returning signal from the compressor (maxed trim, maxed EQ).

Try it!