here is an idea I had a few months ago and posted at another site. If someone would actually produce one of these boxes I'd buy one for certain.
"Here it is, it's a plugin/interface combo. The interface is a set of digitally controlled attenuation circuts. These circuts are all analog and only use digital as a control over the "knob" The plugin part is a track tool that actually lets you draw envelopes to control the all-analog signal path.
8 of these in a box synced to my tape machine would be a dream come true. I could add audio to an 8 track reel machine and then go and edit my analog tracks as well!
On a 16 track machine it gives me dynamic control over 8 channels, make em cascade friendly and I coud do all 16.
Has someone already made this? Seems like it could be done in a reasonably priced rack with a USB connection. "
So basically the audio never goes through a soundcard or computer at all, you just route audio into the patchbox of op amp driven volume controllers. As long as you have your computer synched up to the tape machine it would be seamless. Even if not you could make a cue point and start the program manually and it would be effective enough to automate the track volumes/mutes.