Since this unit is a physical relay instead of opamps then operating it in reverse shouldn't be an issue, but it's best to ask Wobo about that. When the switching is done electronically, then the signal path really may be unidirectional (the input and output impedances won't like being reversed).
The thing that you need to be careful about here is that the flipping relay is not that different than passing the signal through a switch, so you want to be sure that it's really pop-free. The pop comes as the physical switch is flipping - depending on what kind of switch they use, you have to worry that there will be an instant where there will be no signal to the output at all or there will be a moment where both outputs are connected together which may also make a glitch or pop. This is an issue when you're switching guitars or effects boxes between amps too, so I'm sure they have something figured out here. One way to reduce the thump is to put a big capacitor inline in the output which will sort of absorb the transient. That works fine, but will have the effect of changing your tone.
All these boxes are sort of expensive enough that they don't want to just put the simple A/B function there, which is why they have the A+B function as well. When you parallel the outputs of the two preamps I doubt it will hurt anything under normal playing conditions but what will happen is the volume and tone may be unpredictable when they're both on (if it's a truly electronic switch, this shouldn't be an issue at all). I guess you can use it for the big bass jam at the end of the show before all your Alembics are smashed!
David Fung
