Hey @DukeLeJeune ,
My three cents...
To answer your switch position question. Obviously this is dependent on the style of music, instruments, fx, etc.
On my main gig I play 85% electric bass and 15% synth bass with my korg r3 keyboard. We play a wide range of music from 50's to present, but mostly concentrate on dance r&b music, and 80's new wave synth pop. I also use a Future Impact synth pedal to cop some of the 80's stuff instead of using my keys.
Considering all stated above I find it best with both the 1203's and TC112v1 top switch up bottom switch down. Honestly I also prefer this configuration with my electric bass as well. I have found with the 1203's in full nasty mode (both switches up), it can be a bit much for my ears over a 4 hour gig. Also this mode doesn't always play nice when using some lush fx and synth fx. I especially don't care for that setting when playing my korg r3 as well. It just adds a bit too much bite. Definitely need a smoother sound. If I were doing a metal gig or a Rush / Yes type of gig, well then 1203's in full nasty mode is perfect.
Sometimes I wish the 1203 had a bit more top end extension, but in the end, I think I prefer the TC112 more anyway due to the lower and higher end extension it provides, and due to the mids being a bit smoother.
When I play my classic rock gig, my Nordy VPJ5 gets the call paired with the 1203's in full nasty mode because I'm looking for that aggressive mid bark that both the bass and 1203's provide.
So to make a long story long (lol), I really think it depends on the music your covering. But I agree it is great to have options and I'm glad you offer them on your cabs with a flick of a switch.