My suggestion would be that you're using the wrong amp model for the job. The B15 is cool, but is kind of a one trick pony. It sounds great for just what you're trying to avoid!!
The B15 get really vintage sounding with the right tweaking, but really poops out fast if you drive it too hard. If you're playing hard and rocking out, the B15 ain't your amp. I get the best tones out of the B15 by keeping the EQ pretty much flat, and the volume knob below noon or just barely past noon. Let the PA make it loud, these weren't super high powered amps.
The GK model really has a nice tight low end, so does the Blueline. It'll grind in the highs, but as long as you don't make it do anything unnatural, it's a great rock sound. Both the GK and the Blueline do loud rock well, but let the PA handle the heavy lifting and don't boost your lows too much or it'll get ugly.
The Redhead seems to be more midrange voiced, something I'd typically use in a ballad or if I was playing a lead. I usually use a touch of reverb with this amp when I'm playing in the living room.
Keep in mind these are only suggestions. I've yet to use any of them with a drummer, so I don't know for sure which amp will work best for me. Hopefully that'll change soon!!
Also, on the BDDI, try turning the level all the way up. I usually run the level and the blend on 100%, the adjust the drive to taste. That way you don't end up with a million volume knobs in your chain, and end up with gain staging issues (it works for me.).