i use a 303, and when you hook it into the aux return of your mixer you can add effects to any input. you can also sample and loop on the fly for live sets...

my set up:

I do that with my 555 only sh*tty thing is the output volume of the sp is CONSIDERABLY lower than my mixer channels.

I guess its time for a mixing board, however small.

weird, it's considerably louder on my 303, i usually have to curb the aux return knob...

Yeah, thats even at max on the fx return, too.
I can get pretty loud maxxing the sp, too, but I hate to do that.

... on the 404 you can raise the output volume up to +9db I guess by holding CANCEL+START/END/LEVEL and screwing CTRL3... or isn't that enough?!
I do that often to overdrive my shit lil bit and if I work with headphones...

NOICE!
Thanks for the tip.
Im gonna check for that in 555 manual