Is this hearing them with no boosted settings in the treble region? I have heard them once and they were bright sounding(had 1.5db boost at 10k) but on leaving the demo discovered the treble had been boosted somewhat and never got to hear them treble flat. I was disappointed but was a novice with the speakers. In other ways they had excellent bass and presentation in sound. Barely need subs!!
I can't imagine adding 4 subwoofers. And the setting of 150hz for them and cutting the 8c's at 55hz. This seems over the top(150) even with home theatre.
According to D&D no difference in sound between the oak cabinet and custom wood MDF (Studio). Acoustically, the 8c and the 8c Studio are identical. Taken from Dutch & Dutch web site.
I would have thought run subs up to 100hz max. 100hz is the crossover freq in 8c from midrange to bass drivers. You may be in danger of masking the midrange with subs at 150hz point. I know little about Dirac ART.