I just received my MB Quart DSC4125 and will be bridging the amp to 500x2 RMS. My question lies with the RCA inputs. I currently have one set of RCA'S coming off of the subwoofer out on my headunit. Am I okay to put a Y adapter on the left and right RCA then attach them all to the corresponding RCA inputs on the amp?

 

ya that should be fine

 

Don't bother with y-adapters.
Just plug your RCA's into input 1 and 3 OR 2 and 4.

 

yes he can do that if he is just goin to use 2 of the channels but to use the amp to its full potential it would be better (if he can) to bridge 2 channels together. so using 1 sub per 2 channels

 

^When bridging an amp, you only need one input, you don't need to use both.

So he can use it to it's maximum potential -as you say- without wasting money on y
adapters.