yes passives go on your speaker wires , actives go on your rca's
im not sure quite how you mean in your explination ? but basicly unless you put the speaker wires directly into a passive, every time you connect another speaker (be it sub mid or tweeter) you will alter the impedance the amplifier see's .
if it was me i would probably find a small amp (50w) and power the mids +tweets with that using a passive , then use the 150w amp to power the 8"s . should give you more controll over the system and possibly help to make it louder + clearer.