I have a head unit that is 27 RMS x 4. I'm planning to install a 50 RMS x 4 amp. Now do the RMS numbers add up for the wattage? So it mean that I am actually getting 77 RMS x 4 or does the Amp wattage cancels out the head unit's.

 

You're going to plug your amp into your head unit via RCA patch cables. The speaker wires are then drawn from your amp, not your head unit.

so 50 RMS x 4 and you'll have the head unit's power free to power other speakers.

 

thanks lucid, that tells you how much i know about this stuff!!