[LAU] looking for a midi recording softsynth

Hi, I was talking to a friend this morning about a project I thought we could do together. He plays free improv piano/keyboard music - dense patterns and textures improvised in live time. I was saying that in principle it would be possible to record a piece of his music on a keyboard as a midi stream, then feed it through a softsynth in a studio and tweak the synth parameters as it's playing to produce the final piece. He liked the idea, but I'm not sure if there's a linux softsynth that would work like this. What it needs to do is: - produce sounds from a midi stream in real time, with the sound altered by tweaking various parameters (knobs and buttons). - the tweaks should be recordable so that you can play them back and re-tweak them until you get the result you want. - the feature I really want is to be able to set presets for the parameters and then fade between presets in real time. E.g. if there are two presets which both use a resonant low pass filter, I want to be able to move a single slider that moves the filter value from one to the other continuously to create a filter sweep. This is different from a fade at the audio stream level. Does anyone know of anything like this? cheers, andy