I have the same setup minus the 115. However I do sometimes add a 115 at our rehershal room. I always avoid the bi-amp mode and run it in mono (this disables the bi-amp so no need to mess with the crossover ) so as both the cabs are getting the same signal. Although i can still balance it with the balance knob to get an even volume from both cabs. Personally I don't see the point in sending highs to one cab and lows to another if both cabs are full range. This method would work better if you were sending the highs to specifically designed cab for highs only.
I pretty much keep my preamp settings at 1 o'clock for the valve pre and 11 o'clock for the SS pre. I find this gives a nice mix
As for the rest of the settings I usually keep it all flat, sometimes boosting slightly at around the 250hz on the graphic. Occasionally I turn the low contour up a bit if it's sounding a bit too thin.
As Lozz says above, start with it all flat and tweak it as needed.
One thing I always find is that when I'm using the amp at low volumes in the house, I am constantly tweaking it to get a nice sound. However, when at higher volume playing with the band I just turn it up to the required volume and leave it all flat and it sounds great.
Hope this helps
David