Hi NeoFreek!
I hust read your post and thought I'd give you some info to make sure you don't get false hopes. All contemporary head-units boast high outputs, like 4*50W, but these figures are way 2 optimistic...The
REAL CONTINOUS output of those amps is more like 13-15W RMS. RMS wattage represents the key info concerning the power of an amp coz it measures the maximum cont output, not a 200ms max burst output, which you'll never get in ANY working conditions in real life! Head-units use so-called power-packs to amplify the signal; genereally external power amps (excluding supermarket brands) use transistor-based technologies that yield far greater results in terms of pure quality and quantity.
You definetly should install that amp! but make sure your head-unit has a line-out like a stero RCA jack in the back of it! plus you'll need to be carefull when wiring the amp...the net is full of good places with info on DIY!!
As a general rule, serious amp producers under-rate their amps, and only disclose RMS values, not BS MAX output.
About connecting 2 amps to the same loudspeaker: NO CAN DO!! it doesn't work that way, unless your 6x9s are configurable in bi-amp mode...If it is so, I'd definately reccommend you to use 2 identical amps if you wan't some kind of improvement over the 1 amp normal config!
About bridging 2 separate amps into one channel....not really either, unless you have rockfordfosgate amps, which are the
only ones in the market designed to do so...I seriously don't think it's even a good idea to try...IMHO
Hope this helps,
Stefano