wow,

is there a chance the noise had anything to do with the cell phone "brain" being screwed into the amplifier?

the top board you pulled is the preamp section of the DSP unit, the lower is the amplifier section. it looks like the cell brain was screwed into the amp section. did you notice any damage on the bottom of the board?

as to paralleling all those wires together, probably not a good solution for the long term.

try getting a used dsp amp

also ground is brown, not black. some of the speaker positive leads are black trace, with the negative being brown.