I have purchased a HSU MBM-12 to add to my speaker set up with the 990. I also have a HSU VTF-3 MK-3 W/Turbo. Although, I have removed the turbo. I found it to lessen the bass detail within music. It sure added a lot of bottom end extension to the sub though, wow. Anyway, back to my question. Has anyone added the MBM-12 to their 990 surround set up? If so how did you configure the set up for the best obtainable sound? I am currently using both of the 990's sub outs. One to the MBM-12, and the other to the VTF-3. I have set the crossover of the 990 to 150 for all speakers. Then both the MBM-12 and the VTF-3 to out with a 0 phase. My dilemma is such that I am finding that the MBM-12 has added a muddiness' for lack of a better word to the bass. Maybe I need to use one output from the 990. And run a cable to the MBM-12. Set the 990's crossover to 150. Set the MBM-3 to out and then, using a Y cable at the MBM-12, run a cable from the Y to the VTF-3. Then set the VTF-3 to in and the crossover at the VTF-3 to 50. Although, I would very much prefer and not do this. As there are a few negatives within this setup. Any advise would be greatly appreciated.

I can think of a couple of things to try. First, you might lower the 990's crossover point to 100Hz. (You could even back off to 80Hz, which is where Dr. Hsu apparently had it when he first demo'ed the MBM-12.) I'd also make sure to enable the VTF-3's crossover and dial it down to around 50Hz or so (the point where the MBM withdraws from the mix) so that you aren't getting both subs working in the same range.

You might consider experimenting with the phase on both subs. Assuming they aren't both in the exact same position, you may want to try both phase switches at 180 degrees and the two at different settings. One of those four possible settings (both at 0, both at 180, MBM at 0 and VTF at 180, and MBM at 180 and VTF at 0) may yield a cleaner output.

There's no reason that I can see to change your cabling - if the MBM-12 had some crossover network that took the incoming signal and divided it up, that would be a different story, but from what I can see in the manual that is not the case.