^^ Was this while testing at home, or at a show? If the former, as I'm sure you realize, your home stereo is nowhere near as loud as what you'll record at concerts, assuming you record rock or other popular music...
I run 1280c>Church Actives>bb>M10 from time to time and haven't had an issue with needing more gain. When I'm using this combo, it is for louder shows. I suppose it does need a bit more gain than my other mics sets did, but not appreciably more.
Two other things worth noting:
1. I do use the SPSB-10 battery box, which is 12V instead of 9V.
2. I assume you bought the cardiod caps? If so, you do not need bass rolloff with that setup at all. If anything, I wish the 1280s with actives put out a bit more bass.
If you still can't get a decent signal, bump up to the mic in on LOW.