No way I'd run Dynaudio C1 full range. I have large bookshelf speakers and use the high pass filter (80hz) ideally would like to play around with adjustable high pass but it's fixed. At the very least set the C1 to 45hz, 50hz etc and bring up the sub to that. My bookshelf speakers go down to 42hz +/- 2dB
My Lexicon can do LFE + Main bass but it's not recommended, as you get duplicate bass. If you have av amp or av pre-amp I'd probably use small 60hz, trying each step between 40/50/60/70/80 and see which works best.
If you use a analogue hifi pre-amp, try and use a high pass filter, take out low bass before the amp stage on the L/R signal, that goes to sub, then pass on higher frequencies to the power amps.
Works very well, like I said, use a subs high pass. Sending full range to C1, plus LFE plus L/R full range to the sub is the wrong way of doing it.