For situation 1 and 2 you would probably want a separate IR Cab sim loader pedal/device, beside the preamp, or a preamp with some sort of cab emulation build in, IR based or not (IR capability would allow for more versatility and tailoring to your specific needs and taste), that gives can be turned off when using the preamp with your amp and cab.
A separate IR Cab Sim loader would give the greatest versatility and result I think, and would probably be what I would do.
Or get something like the "Two Notes Opus" DI, Amp & Cab Sim (all in one solution, sounds amazing, and very affordable for what you actually get).