Stacking eq presets

[tryonkus]

Description:
I really like that I can look up my Logitech headphones and load a preset to correct their response; however, I purchased eqMac primarily to correct for my hearing loss. I'd like to be able to stack my audiogram and the headphone preset and be able to turn each on and off independently.

This is related to but not identical with #939

User flow & interface:
This would be an enhancement to the existing equalizer.

• I can create presets for both my headphones and hearing correction and load them individually.
• My initial thought was to stack equalizers or to use an Apple equalizer on top of eqMac, but it occurred to me that it would be possible to simply add more EQ channels (in Expert mode).
• One possible interface design would be to allow multiple presets to be selected simultaneously via command-click, then activate the EQ channels for both.
• It could be possible to differentiate the channels for each preset by using color coding or by inserting a divider between the two sets of channels.
  • This would not be a necessity, but it could be helpful. It would be necessary if the multiple preset method is not implemented.