What is the end goal you are trying to achieve? Louder over all playback levels, more thump? The 8C’s appear to have a sub out, is it full range or do they have low and high pass filter capabilities? The drivers in the 3070’s appear to be on angled baffles, are you using them in a side firing configuration or a front and back configuration? Are the 3070’s currently in the room now and if yes are you having any issues?
The first potential issue that jumps out to me could be a phase issue. A lot of drivers facing different directions, specially if the 8C’s are run full range. Potentially a lot of different paths for the sound waves from different sources to take on their journey to your listening position could make for some muddy bass.
The another possible issue if the 8C’s are full range is that your subs may not have much to do. According to the 8C’s spec’s they are good down to 30 Hz, not much in recorded music gets that low, not too mention lower.