Hi tgonzales,
I too have 3.7i's and DWM's. Some questions, as I got confused on the details.
By parallel, I think you are stating that you run one set of wires to the main speakers out of one set of taps and you run a second set of wires out of the second set of terminals. That is how I have always run my DWM's.
When you say "series and parallel" in the same system are you saying you ran a set of jumpers from one half of the DWM to the other half? Wouldn't that imply a 1 ohm load? Or have I Misunderstood?
the only time I have used both sides of the DWM at the same time is when I run a single one, in which case I connect the right channel to half and the left to the other half. (For those not owning DWMs this gives the volume of two DWMs with a single unit, but restricts placement options).
I will say that even driving half the DWM out of the second speaker taps can result in muddy sound in my system. It is easy to get too much lower midrange and too much upper bass (I have never heard ANY benefit below 63 hz of using DWMs). They recommend placing the DWM 10 inches loser than the mains, and this does help, but I suspect it also messes up the coherence of the back waves, which are now clearly lagging (by my thinking if the front wave is lined up ten inches closer then the back wave is off by twenty inches?).
two things which I have found help. First is I use resistors to lower the output of the DWM, and second I find that I can get less bloat in the bass by running them exactly parallel and on the outside of my mains. Since my mains are pointing directly at my ears, the DWMs are effecyively the same distance. This tightens the bass up, but does not always work, as I can sometimes get peaks (depending on where my main speakers are in the room).
How do you have yours placed in comparison to the mains? Are you using resistors or attenuators?