wiring a capicitor in a dual amp system

Agree with the above, but just for the sake of answering your question about where the cap should go if you intend to use it:  it should be as close as possible to the sub amp(s).  It can be wired as you described, although it seems like it might be farther away from the amps than is optimum.  The distro block is a "splitter" itself, so you have, in effect, two splitters.  One of them can be eliminated. 

Ideal (with what you have) is to run main power wire to a fused distro block that is located near both sub amps.  The cap is placed directly before the distro on the main wire, and the distro's two outgoing fused smaller wires lead a short distance to each amplifier.

Power connection devices like distros should be mounted in open, easily accessible areas rather than hidden under the seat.

you need to relearn the tach signal on the alarm. if its a DEI alarm (viper, clifford, python, hornet, etc etc etc) the steps for relearning the tach are as follows:

start the car

within 5 seconds push and hold the valet button

when your LED goes to a constant light, the tach is learned (usually only takes 3-8 seconds for it to learn the tach)'

release the valet button

and thats it....if you don't have a DEI alarm, then it could be an entirely different combonations of things....

good luck.