Once again as stated the Rumble Filter and Air switch were designed for acoustic guitar applications. You can certainly try to use those features with other instruments if you wish but the Rumble Filter's
RUMBLE FILTER
Engaged (in position), it removes unwanted sub-sonic frequencies that cause boominess and audible handling noises associated with acoustic guitars. Also complements other instruments, such as electric guitar, for a snappier, more inyour-face sound. Note: When Blend is at minimum, there will be no effect.
AIR
Engaged (in position), adds top-end clarity and sparkle to acoustics. Also complements other instruments, as well as vocals, for more definition and more open sound. Note: When Blend is at minimum, there will be no effect.
The Bass Driver, Para Driver and VT Bass DI's are amp emulators that can also be used as standard transparent DI's if desired when bypassed. They are flat response when bypassed. If engaged with the blend control off and the EQ's set to their null points they are also flat response and can be used as a DI with added EQ.
When the Blend is set at 100% the SansAmp circuit is engaged adding amp and speaker emulation which is the point of the product.
For myself I just plug the pedals in, listen to my sound in bypass then engage the SansAmp and adjust for the sound I desire. I'm lucky in the fact that I have access to all our products and can easily try them back to back but for the most part I can usually find a workable sound fairly quickly. I could ask our designer or engineer to put the pedals on the FFT or connect them to an oscilloscope but that seems somewhat pointless to me and a waste of time. It's much faster plugging in, playing and trusting what I hear vs looking at a computer screen. All our products are tuned by ear, measurements are used after the fact to ensure consistency from the prototype to production as well as for troubleshooting.