is the cable that runs to the bottom of the engine a ground cable? As far as the alt is concerned there is no such thing as too much as long as it isn't a 16 or 24 volt alternator. Add up the total fuse sizes on both of your amps and that'* how many amps your alt should be able to put out. For example if my 4 channel has two 25 amp fuses and my sub amp has a 150 amp fuse my total fuse size is 200 amps and that'* what my alt should be able to do. But the amps would never pull a total of 200 amps or the fuses would blow so if you had an alternator that did a little less it'd be okay and if yyou had one that did more it would only put out what'* demanded of it so you'd be fine

Ok thats what i was worried about, i didnt know that you could get 16 and 24 volt alternators. The cable is on the positive battery terminal and goes down to bottom out of sight.