Hello All Amiga Fans (rusty amiga guy NEEDS your help!)

[amigagr]

check here for the hd. at search type A500-HD+ Impact Series II to find the controler. as it says it needs a psu.
welcome to amiga.org :-)

[amigagr]

probably the one side must be a middle jack and the other 2 rca red and black or red and white.

-edit-
yes you connected as you say

[amigagr]

not exactly, this combination is an international standard but maybe this cable is hand maded. that can means too that maybe a wire is broken from one side or the other. you can buy one set from a local store for no more than 3 euro, so don't worry a lot for the moment :-) just ask for stereo middle jack to stereo rca.

[amigagr]

i don't know what exactly you mean but in general when you shift a channel up or down you shift both video and audio, as for example happens in video tape devices.