I've got a Mazda Miata, and this is what I've got, and how I want it to work.... At least how I think I want it!
Clarion 835MP Headunit
CDT 6.5 Components in the doors
Soundstream 5 channel amp EGA5700 50wX4, 200X1 rms (4ohm)
Aura Bass Shaker for seats 50w 4ohm each (one for each seat)
One Image Dynamics ID8v3 Subwoofer 300w rms DVC 4 ohm each voice coil.. In a small box in passenger footwell. No trunk sub for me!

I want to hook everthing up so the following applies...
CDT on front channels, 50w each... this is the simple stuff..

I'd like each Aura Bass unit in each seat to get 50w too... these need to have low pass at around 100 or so... I'd like to control this with the subwoofer level controller on the headunit...

The sub will go on the sub out of the amp at 2ohm, receiving 300w rms... I'd like it to be controlled with the sub level controller as well...

I know I might get flamed for using the bass shakers... but this is a very small convertible, no room for bigger subwoofer... I figure they'll help the low frequency out, what the 8" sub can't generate...

The headunit has sub crossover at 50, 80, 120, or it can be full pass...

So options are (as I figure it) as follows:
CDT's on channel 1,2 on front outputs,
Bass Shakers on 3,4 using rear outputs on headunit - using fmod crossovers in RCA cable to allow only low pass
Sub on sub channel... this would give me fader control to bass shakers but no control thru subwoofer control. I'd have to use HP crossovers on amp to control front channel. There are no LP crossovers on rear channel so I'd need the FMODS. Headunit crossover could not be used or would remove bass from rear channels..

OR...
I can have CDT's on front, nothing on rear RCA outputs, then split sub RCA cable at amp with one pair to rear channels, another pair to sub outs... this would give me control of both sub and bass shakers with sub control on head unit... since this would be under headunit crossover it should limit freq. to the bass units.

OR...
CDT's on front, set the bass shakers and the sub up on same channel, wired in such as way as to get 4ohm, leaving rear channel open. Only concern here is all three would get same amount of power (?)... if the bass shakers were wired series to 8ohms, and the sub wired parallel to 2 ohms, them both circuits wired in parallel (would this be 5ohms?) - would this work, or would it destroy amp, and would I get more power to the sub, less to the bass shakers???? This is where I get confused...

OR...
should I just install the bass shakers on a second amp, possibly sharing the RCA feed off the headunit... I do have an old JVC 2 channel amp.. I wouldn't think the quality of the amp feeding the bass shakers would matter too much...

Any idea what would be best? Or other suggestions?
thanks for your time,
ed