For doubling, I can't turn the volume down on my upright. My amp has a mute switch on it for each channel, but for instruments without volume knobs, a mute switch is a necessity. Otherwise, my upright will pick up anything and everything it "hears" when it's not being used.Bassdude is not a D.I., but it does have a bypass switch. Nobelium is a D.I. and you may be able to find room inside the box for a mute switch, but it certainly wasn't designed for it. Grand Slampegg's design has not been finalized.
As I have zero experience as a gigging bassist, can you explain to me why a mute switch would be important in a D.I.?