When you say full Blam speaker install with no sub did you replace the woofers in the foot wells? I think this could be a weak link in my current system. I have just got front door replacement speakers so far (4 inch drivers plus tweeters) and I think my car only has one factory fitted speaker in the passenger well.
I did replace the woofers too. In actual fact, it's not really a full Blam setup as I only replaced the fronts (two in each door) plus the footwell woofers.
The rear speakers are still stock, and I haven't got a center either. So it's half a full setup
Do you have the Audio20 or the Burmester? I could be wrong but I think the non-Burmester system has a single woofer (can't remember the size, either)
The footwell subs are worth doing, especially if you have a DSP I reckon. They do kick much more than the stock ones so I'd expect Ground Zero to be similar.