does this product exist?

I am looking for a "black box"/signal processor to time-delay my speakers.  All of the products I have researched have one major drawback that I just can't live with...you have to set up the system once, then use the PRODUCT'S volume control knob,etc. to adjust volume from that point on.  No more using the steering wheel controls or head unit for volume after that.

Does anyone know of a unit that I can use to set time-delay, and still be able to use my head unit's/steering wheel volume control functions?

Thanks in advance.

Sorry for the ommission...

Stock BMW "Business CD" HU, all else aftermarket.

Ah.  Well, I suppose if you must use the stock HU you could still use any LOC on the speaker outputs then run those line level signals to an outboard processor like the Alpine.

But, the Alpine is the same way, correct?  Unable to use the OEM volumes once you set it up?  That's the impression I'm under...no?

Hmmm, now all I need is a second income!!  ($450)

Thanks, consider my question answered enough for me to keep looking!